If I rent a Minecraft server, can I load mods on it?
That depends on the respective provider.
Nitrado
That's fine. Here is a tutorial on how to do this: https://wiki.nitrado.net/de/Mods_auf_dem_Minecraft_Server_installieren#:~:text=Logge%20dich%20in%20dein%20Nitrado,richtig%20auf%20dem%20Server%20installiert.
Yeah that works
Why Nitrado?
That's way too overpriced