What is version 0.11.3-1.16.5 minecraft?

Is it possible to actually download mods with all versions?

Yes, with all of them, but whether they are compatible is another question

Because there's Fabric loader and then the version

Exactly, and the version means that you need a specific version of Minecraft for the mod

The 0.11.3 is the version of the mod. The 1.16.5 is the Minecraft version. Some mods for 1.16.2 / 3/4 are also compatible with 1.16.5. Mods for 1.15 and earlier are not compatible with 1.16.