I assume you're talking about his time in the Spanish Civil War. But even then some of his contemporaries saw him as essentially an unserious war tourist who was in Catalonia just to collect juicy material for his writing.

Orwell had no understanding of the world-wide significance of the struggle in Spain, he knew little of the national efforts of the Popular Front government to achieve a united front against fascism, he had never seen the Republican flag, he did not agree with the actions of the POUM — he took a rifle in the role of an outsider, a journalist looking for experiences to figure in a future book.” — Bill Alexander, commander of the British Battalion of the International Brigades during the Spanish Civil War, in George Orwell and Spain (1984), p. 94.

Not to mention his supposedly negative review of Mein Kampf. Yeah, he shit talks it super vaguely here and there ("Then suddenly it turned out that Hitler was not respectable after all." I've heard of ironic understatement, but don't you think you're overdoing it just a little here George?), but then he somehow finds it possible to say that he doesn't personally dislike a literal genocidaire and spends so much time talking about Hitler's supposed supernatural "charisma":

But Hitler could not have succeeded against his many rivals if it had not been for the attraction of his own personality, which one can feel even in the clumsy writing of Mein Kampf, and which is no doubt overwhelming when one hears his speeches. I should like to put it on record that I have never been able to dislike Hitler. Ever since he came to power—till then, like nearly everyone, I had been deceived into thinking that he did not matter—I have reflected that I would certainly kill him if I could get within reach of him, but that I could feel no personal animosity. The fact is that there is something deeply appealing about him. One feels it again when one sees his photographs—and I recommend especially the photograph at the beginning of Hurst and Blackett's edition, which shows Hitler in his early Brownshirt days. It is a pathetic, dog-like face, the face of a man suffering under intolerable wrongs. In a rather more manly way it reproduces the expression of innumerable pictures of Christ crucified, and there is little doubt that that is how Hitler sees himself. The initial, personal cause of his grievance against the universe can only be guessed at; but at any rate the grievance is here. He is the martyr, the victim, Prometheus chained to the rock, the self-sacrificing hero who fights single-handed against impossible odds. If he were killing a mouse he would know how to make it seem like a dragon. One feels, as with Napoleon, that he is fighting against destiny, that he can't win, and yet that he somehow deserves to. The attraction of such a pose is of course enormous; half the films that one sees turn upon some such theme.

(Side note: really suspicious that when I googled for Orwell's review, the versions in the top results always seem cut out the part where Orwell says he never was able to dislike Hitler.... )

And his ending paragraph, ostensibly meant as to criticise the fascist false promise of providing with meaningful struggle in a nihilistic world, actually spends more time puching at "hedonistic" Socialism (Socialists want peace and sustainable material improvements for the lives of the working class? Oh horror!) and while also doing false equivalency between Stalinism and Nazism:

Also he has grasped the falsity of the hedonistic attitude to life. Nearly all western thought since the last war, certainly all "progressive" thought, has assumed tacitly that human beings desire nothing beyond ease, security and avoidance of pain. In such a view of life there is no room, for instance, for patriotism and the military virtues. The Socialist who finds his children playing with soldiers is usually upset, but he is never able to think of a substitute for the tin soldiers; tin pacifists somehow won't do. Hitler, because in his own joyless mind he feels it with exceptional strength, knows that human beings don't only want comfort, safety, short working-hours, hygiene, birth-control and, in general, common sense; they also, at least intermittently, want struggle and self-sacrifice, not to mention drums, flags and loyalty-parades. However they may be as economic theories, Fascism and Nazism are psychologically far sounder than any hedonistic conception of life. The same is probably true of Stalin's militarised version of Socialism. All three of the great dictators have enhanced their power by imposing intolerable burdens on their peoples. Whereas Socialism, and even capitalism in a more grudging way, have said to people "I offer you a good time," Hitler has said to them "I offer you struggle, danger and death," and as a result a whole nation flings itself at his feet. Perhaps later on they will get sick of it and change their minds, as at the end of the last war. After a few years of slaughter and starvation "Greatest happiness of the greatest number" is a good slogan, but at this moment "Better an end with horror than a horror without end" is a winner. Now that we are fighting against the man who coined it, we ought not to underrate its emotional appeal.

Orwell's not a commited anti-fascist. His worst condemnation of fascism is merely of its aesthetics, and his tepid opposition to Nazi Germany is just another opportunity for him to posture and smear leftists that are more serious than he is in defeating fascism.