Quake 3 Arena is still available for sale on
GOG, and ioQuake 3, the open-source modernized port of Quake 3 Arena/Team Arena, now supports
Apple Silicon through a new set of universal binaries.
It is unfortunate that the classic Unreal games have been pulled from sale - likely in the near future Epic will re-release them for sale as "Remastered" editions exclusively on the Epic Game Store.
In the meantime, depending on how desperate you are, you could possibly try to find a copy of the Unreal games for sale on eBay, or Steam/GOG keys for the games on sale on places like G2A or Kinguin. (If you're willing to risk potentially getting scammed by an unscrupulous key reseller.)
If you're looking for free Quake-ish competitive twitch-style shooters,
OpenArena,
Rexuiz,
Xonotic and
Warsow are all based off of various flavors of Quake's underlying engine technology.
AssaultCube and
Red Eclipse are based off of the open-source Cube engine.