I'm glad I am not the only one. I've spent a few hours trying to figure this out myself.
I have tried installing a few MLO's, edited the dlclist.xml file and placed the dlc folder into the dlcpacks folder. Yet lately they dont work.
I've used the Foodshops mod and it works no problem.
I think it might have something to do with the most recent update possibly? Im not sure.

I'm installing this one. Its pretty simple install yet I'm not getting any results when installed properly.
https://www.gta5-mods.com/maps/mlo-lost-mc-bar-paleto-bay-add-on-sp-fivem-altv#description_tab The version of this mod I am trying to install is the SP version.
I'm running on a legit copy of gta 5 via the epic games store.