Based on what you could buy through distributors, less than 5% of the STM32 lineup is available to buy. The situation was worse, 6 months ago there were 27 variants available on Digikey of the 3000 or so they make.
The G series seems to have good availability at the moment, if I was going to bet on a MCU for a new design that would be it. L series has only just gotten better, couldn’t get them a few months ago.
Some F3 chips have been looked over (didn’t go out of stock) despite being more advanced than their F4 counterparts. That’s marketing I guess.