The vast infrastructure that is necessary to keep jets in the air is not something one can replicate overnight. Since the idea of building an airbase in or near the Ukraine that could keep F-16s in the air is ridiculous, will the F-16s fly off of a US aircraft carrier in the Black Sea? Will the Ukrainian pilots just fly the jets until they break, then eject, saying ‘oh well’ thanks for the memories. C’mon Man!
Both Poland and Romania operate F-16’s.
So “near Ukraine” is not a problem. If a Ukrainian F16 needs more intensive service it’s not far away.
And the real issue with service isn’t parts or equipment, which can be bought or donated, it is personnel. And Europe is full of experienced F16 maintainers that could easily be hired to work in western Ukraine and besides servicing F-16s, do a train the trainers thing with the Ukrainian AF crews.
F-16s cannot launch from aircraft carriers.
Secondly, just as in Afghanistan, service and support is done by US Contractors with very lucrative contracts that kick back to politicians.
The US uses contractors because the key technology is not trained to foreign support personnel that can be hired by China.