i just use pacman, mean it has checksum tests after downloading since youre only really downloading the launcher

i agree with everything, but calling cuba tiny is a bit of an understatement, cuba is about the size of portugal or bulgaria or hungary or south korea (not combined, individually)

i only ever used arch linux idk how other distributions handle it

try installing ffmpegthumbnailer and see if that works after reboot / relogin, if not uninstall and try another method