Hello @danimatias23
You can try verify your files:
Steam>Library>Ets2>Right Click>Properties>Installed Files>Verify integrity of game file.
Your game files be verified and join game try your question solved.
I recommend using custom graphics settings instead of the available presets Low-Medium-High-Ultra. However, what you can do is changing the game resolution to 125% or 150%, and the rest of the settings to low, especially the quality of the grass and vegetation in general, that affects the performance a lot. As for other settings, you can try changing some of them from Low to Medium based on how that is affecting the performance.