when I open the source lifetimer, it appears in the system tray and can be found by Obs, but I can not see it on my screen

The source lifetimer is the timer that calculates how long you have to live.

i've had that problem before. there are 2 solutions to it: 1- you gotta delete some file somewhere that saves where you last left the window on your screen (i don't remember where said file is, which leads us to solution 2); 2- rename the folder in which the livetimer is/move the timer to another folder

Solution 1 btw: https://github.com/iVerb1/SourceLiveTimer/issues/1