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.
No there are still tens of original UAF jets that by now clocked thousands of sorties. Sometimes they get shot down or otherwise lost and we get photographic evidence (tail number, sometimes even pre-war colors) that it's one of the OGs.
https://en.wikipedia.org/wiki/Aerial_warfare_in_the_Russo-Uk...
https://aerospaceglobalnews.com/news/how-many-aircraft-losse...
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.