From looking at the sources below, it looks like Ukraine still has about 1/3 of the fighter aircraft it started the war with, though it started with many non-serviceable units (seems that at least 20 aircraft were non-operational), and received many parts from abroad:
I am not sure what is meant by 'a significant number of', and I'm not sure if all commenters have a common definition of that phrase, so I'm unable to judge the veracity of the comments above.