Can someone outline the differences between the two versions (except multiplayer functionality)?

There are two versions in the launcher with virtually no difference as far as I can tell. And then in the multiplayer menu what exactly is the difference between the two there? Does that mean there are four "different" versions to play the game in multiplayer in or how do I have to understand that?

Meet us in the multiplayer Battle Net server in channel Classic Games

The enhanced is a version with some quality of life and improvement for playing campaign made by GoG. While Classic is the online play if you want to play Multiplayer online.

If you chose to come online on GoG Global battle.net server, do meet us in " Classic Games " channel once logged on as Steve_Paul_Hansen said.

Cool thanks, is there are list of the improvements somewhere?

I played the enhanced version only a little bit before switching to classic b/c of the mouse problems, so I did not really notice any improvements. Would appreciate if someone could list at least some of them.

Well I do notice some strange behaver with the flying units in the Enchanced version, like the second campaign of the humans in the exp. the yellow orcs did not send any dragons at all. And sometimes in other missions the AI keeps spamming them (feels more like the vanilla version, the last mission of the normal human campaign is very very annoying with the constant dragon spawn of white and 3 dragons of orange)

Enhanced just crashes at startup so I stick to classic.