If u wanted to play terraria AND modded terraria (let’s just say it works for 126.96.36.199), before downloading tModloader you’ve had to make a copy of the normal terraria and rename that to something thats not terraria.exe. What tModloader does is it modifies the actual terraria.exe with its files. However this is not permanent. If you take away everything that starts with “start-tmodloader”, “tmodloader installer”, and “tModloader server”, it should work fine. If it doesn’t, then im wrong and you jsut need to reinstall Terraria.
Also don’t delete Terraria_unknown.exe. Is it in the same file folder with Terraria.exe?