Mods don't work in 2.81 and if you actually try to go into the mod menu while in game it crashes to desktop once you start pressing buttons. If you want mods to work in the remake just use 2.64 from itchio
Technically mods do work, but not in the mod section. So far there is only 1 mod for 2.8, and it can be played by putting it into the act 1 folder, whrere it will replace Cathy. (you can use the CFG file in act1 and copy and slightly edit it to be able to make a new act, where the mod will also work)
So you basically treat the base levels as being a mod, and just go from there.