As in summary, tg_owt appears require x11/libXtst for buiding, so that USE_XORG = ... xtst had to be added.
Excerpt of poudriere build of net-im/tg_owt:
CMake Error at /usr/local/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
Could NOT find X11 (missing: Xtst)
Call Stack (most recent call first):
manually installing libXtst in poudriere jail build makes tg_owt compilation successful.
Hm, I think you're right: it asks for xtst, and also xext, actually.
On the other hand, the port builds fine in poudriere etc. I suspect xtst and xext are required by other ports, while the build options you set may removed these dependencies.
In general, I agree that both xtst and xext should be added to the USE_XORG list.
See the cmake file for details: https://github.com/desktop-app/tg_owt/blame/master/cmake/external.cmake#L227
Yes, i did look at upstream cmake, after encountering build failure. Honestly, i would like to have X11 support to be optional in both tg_owt and telegram-desktop but it is another topic.