All Kindles I had (the latest is paperwhite from 2020 or so) mounted on USB as mass storage and supported pdf. They also supported epub since 2014 at least.
You're wrong about that last bit. Kindles still don't support just dropping an ePub into their storage -- you have to convert to a supported format first, either manually (or through Calibre), or by using the Send to Kindle service to get them into your Amazon library. Said service only started supporting ePubs itself in late 2022, also.
