There is a lot more than 4 clients out there. For example I develop Nheko, which supports E2EE (including cross-signing) as well as 1:1 calls (those only on X11 though, because time and none seems to be interested in adding call support on other platforms). Then there are UX improvement forks like SchildiChat, clients for other platforms like SailifshOS, etc. Oh, and I almost forgot about Mirage.