Some of the Rightists religiously try to portray Bose as a Leftist (and thereby make him a symbol of their ire and hate) because they hate his association with Muslims and his love for Hindusthani. Such Rightists are a product of indigestion of India's culture, legacy and heritage. They merely emulate the Leftists whom they hate and have no intellectual boda fide to even compete with the leftists that they ardently hate. Because with due respect, many brilliant academics and artists had been ardent Leftists, but I am yet to find a brilliant rabid Rightist - they are sooo mediocre, most of them, that it is little surprising that they hate Subhas Chandra Bose. Some of the leftists and communists, who are not entirely allergic to Subhas, are able to forgive him for his "transgressions" in terms of aligning with the Nazis and the Imperial Japanese. They claim Subhas Chandra Bose as their own in terms of ideology, although they do not bother to explain the aversion of their fellow leftists and communists towards Subhas Chandra Bose. Indian leftists and communists in particular are distinguished by two traits - 1) Their aversion towards National interest and anything pertaining to Nationalism, which they disdain on account of their apparent "universalism" (which, if you ask me is their biggest lie - as one cannot be universalist by picking on and eliminating the "class enemies", a universalist should be a lover of humanity, communists most certainly are not - they are lovers of their own party and ideology though). 2) Leftists deride and disparage anything associated with our Indian civilization and culture. They are in general Hinduphobic, and hold Hindus responsible for all ills, support or at best trivialize the perpetrators of Hindu massacres like the 1971 genocide of Bengali Hindus or the Kashmiri Pandit genocide. They deny any achievement of Hinduism, including ancient Hindu traditions, the spirituality of the Bhakti movements, the lofty philosophy of Samkhya and Vedanta, and glorious traditions of the ancient Hindu kings. Their whole history begins with the advent of Islam and they leave no stones unturned to establish the glory and superiority of the Mughals. So the leftists in general (there may be exceptions no doubt), decry our glorious culture, tradition and past. Ramayana and Mahbharata are to them mere "mythologies" and according to them the true history of ancient India began with Buddhism.
Now the key question is, was Subhas Chandra Bose really a leftist? In a traditional sense if we go by points 1 and 2 distinguishing the leftists from the saner people, the answer is a resounding no. Subhas Chandra Bose's own writings, esp. his Indian Pilgrim, also bring out the fact prominently that he, while not being blind to the obvious limitations, loved India and its culture and the traditions. He was no apologetic. He was fiercely and staunchly Nationalist, much more than the so called Nationalist leaders of Congress. He had great respect for the spiritual tradition and wanted to embrace the life of asceticism at an early life. He was particularly inspired by Ramakrishna Vivekananda ideology. He actively fought for the right to hold Saraswati Puja and Durga Puja and even performed the ritualistic worship, carried his pocket Gita and Chandi everywhere he went and was initiated in Kriya Yoga by Baradacharan Majumdar. He was also associated with Tantra and had great interest for Vedanta. He praised Shivaji - a hero of the Nationalists and decried fundamentalism of Islam by calling out the hypocrisy of Muslim League and the Fazlul Haq Government of Bengal. Although he entered into a tactical alliance with Muslim League and his guru Chittaranjan Das made the famous Bengal Pact, both of them were staunch realists. They knew that with only 40% Hindu population, the only way to save Bengal from fanatic, rabid Islamists was to give them certain concessions while maintaining the rights and the privileges of the Hindus. Bose was no exception as Shyamaprasad Mukherjee also entered into a compromise with Haq and accepted a ministry in his Government. So Subhas Chandra Bose differed from the traditional leftists and the Communists on both points 1 and 2. He was not enamoured by Russian revolution, he only weighed Russia as an option against British Imperialism. He had seen Europe from close quarters and was not impressed by the European Communists, particularly the British Communists, although he tried to seek their help as well for the sake of India's interest. In a very well written article (https://www.firstpost.com/india/subhas-chandra-bose-the-myths-the-distortions-and-the-biases-2614570.html?fbclid=IwAR2DD3YRiGf8-l7u_NMsZmEncNeYrJfDJ1KUHxLVDhafbM2anaz0Iast83c) Saswati Sarkar et al points out the views of Subhas Chandra Bose on leftism in general and Communism in particular. Their conclusion is Subhas Chandra Bose can be considered as a Socialist in the truest sense - that he really cared about the rights of the underprivileged, the farmers, the trade unions and other poorer classes. But he wanted to lay emphasis on heavy industrialization, scientific and material progress and rationalism as opposed to Gandhian socialism that depended only on village based small scale industry development with little or no progressive and modern outlook. As Subhas writes in Indian Struggles - "There are several reasons why Communism will not be adopted in India. Firstly, Communism today has no sympathy with Nationalism in any form and the Indian movement is a Nationalist movement – a movement for the national liberation of the Indian people. (Lenin’s thesis on the relation between Communism and Nationalism seems to have been given the go-by since the failure of the last Chinese Revolution.) Secondly, Russia is now on her defensive and has little interest in provoking a world revolution though the Communist International may still endeavour to keep up appearances. The recent pact between Russia and other capitalist countries and the written or unwritten conditions inherent in such pacts, as also her membership of the League of Nations, have seriously compromised the position of Russia as a revolutionary power. Moreover, Russia is too preoccupied in her internal industrial reorganisation and in her preparations for meeting the Japanese menace on her eastern flank and is too anxious to maintain friendly relations with the Great Powers, to show any active interest in countries like India. Thirdly, while many of the economic ideas of Communism would make a strong appeal to Indians, there are other ideas which will have a contrary effect. Owing to the close association between the Church and the State in Russian history and to the existence of an Organised Church, Communism in Russia has grown to be anti-religious and atheistic. In India, on the contrary, there being no association between the Church and the State, there is no feeling against religion as such. Further, in India a national awakening is in most cases heralded by a religious reformation and a cultural renaissance. Fourthly, the materialistic interpretation of history which seems to be a Cardinal point in Communist theory will not find unqualified acceptance in India, even among those who would be disposed to accept the economic contents of Communism. Fifthly, while Communist theory has made certain remarkable contributions in the domain of economics (for instance the idea of state-planning), it is weak in other aspects. For instance, so far as the monetary problem is concerned, Communism has made no new contribution, but has merely followed traditional economics. Recent experiences, however, indicate that the monetary problem of the world is still far from being satisfactorily solved.’’ pp. 352-353, The Indian Struggle (1920-1942).