Had the same issue and found a quick resolution here on the Steam forums. Real quick thing to do by changing your setting for fullscreen before loading up the game. Only have to do it once as it is fine every time afterward. Why SWTOR did this to some people after reinstalling after some time away from the game, who knows...
https://steamcommunity.com/app/1286830/discussions/0/2796125386567745482/
Post is near the bottom, dated July 8, 2021:
FYI, I had the same problem and found a solution.
This seems to occur when I close the game while running in "Fullscreen - Windowed" mode. Trying to launch again from Steam shows the splash screen but it's frozen and never advances to the game (the little gold gear icons in the lower right hand corner don't spin, which is a clue that the game is bricked).
The solution I found is to make sure SWTOR is closed; open the client_settings.ini file (c:\Users\[Your_User_Name]\AppData\Local\SWTOR\swtor\settings\client_settings.ini) in a text editor. Find the line that reads:
FullScreen = true
(Around line 19) Change it to:
FullScreen = false
Save the file and start the game.
The game will then load and you can go back into your settings and set your graphics up the way you'd like.
Hope this helps.
Quick note: If your file does not have a line for Fullscreen = true, then create one yourself and use the false ending.
@5a04244ab577f26444ae0810c640f109
Easier directions to the client_setting file can be found in the guide https://answers.ea.com/t5/General-Discussion-Technical/Guide-Game-failing-to-launch-on-Clicking-Play/m-p/4809830/highlight/true#M70795
Press the [Windows] Key + [R] at the same time
Copy the following in to the text box and press ok
%localappdata%\swtor\swtor\settings
Open the client_settings.ini file in notepad and ensure the following are displayed within
Fullscreen = false D3DFullScreen = false RefreshRate = 60
Check NativeHeight, NativeWidth, Height and Width ( all 4 ) match your monitor resolution.
Save and close the file.
Start the game as normal.
Change graphic settings within the game as desired.
