Please use MTAsa Diag and put the codes here
https://forum.mtasa.com/topic/124035-i-run-the-mta-sa-and-it-opens-gta-sa/
Had this issue with the Rockstar launcher before. Move your GTA files to your Programs x86 folder instead of just programs. That's what worked for me.
Everything is fine, but let me give you an options to try. Uninstall your MTA then Reinstall your MTA to a different/wrong GTA SA folder. Then Reinstall again to the exact folders.
Where does the shortcut point to? Right click MTA icon then do > open file location, does it bring to you GTA:SA install folder or MTA install folder? Awkward issue you're having there.
Hmmm, uninstalling MTA and GTA (both) completely and re-installing might solve your problem IMO.
Deleting everything related to mta and GTA then redownloading both will be the solution then?
Do you have a GTA-SA-looking file called proxy in your GTA SA directory? If yes, try deleting it and open launcher again.