Seconding for SWAT4. It’s available on GOG and still has an active modding community. Imo the AI is better in this game than in Ready or Not, although RoN is certainly more visceral overall.

You can get the earlier Arma games up to A2 on disc which afaik don’t require steam, they run from their own launchers. Arma 3 has a physical edition as well, but during activation you have to link to Steam.