Yes, TFGM only works on Windows systems, so if you are using Linux or Mac you can’t use it.
Just moving the mod to the mods folder only makes it visible in TF’s mod manager. You still need to tell TF that you want to use the mod too (activate it).
Start TF.
Go to “New Game”
Click the “Advanced” tab.
Now you should see two list boxes, to the left the available not yet active mods. To the right the selected and activated mods. Use the arrow buttons to move mods between them.
Press start to begin a new game with the active mods.
However, if you run Windows, you can activate the mods in TFGM by selecting the installed mods and press the activation button. TFGM have an 80+ pages PDF manual for download from TFGM’s “official” page:
https://www.transportfever.net/filebase/index.php/Entry/486-Train-Fever-Game-Manager/