I’m writing this from a small 20 tent only campsite on a Croatian island. Access is only by ferry. Facilities are limited (no large supermarkets for example). It’s our third summer here and while there have been some changes, it is very slow.
Taking a boat out for a day or two also allows for exploration of other, more remote islands. Some bays still aren’t over crowded with boats anchoring for the day.
Also, later in August and early in the week are quieter times. Yesterday, I was the only person swimming at a nice sandy beach at 14:00.
Greece is unique in it's own way - but it's the OG tourist trap in the area.
Coast of Italy isn't really comparable on the Adriatc side (haven't been to Sicily so can't really compare)
And Montenegro is 100x more overdeveloped and touristy. I’m not sure where exactly you are referring to.
Communicating with locals over 30 is a bit challenging unless you know Albanian or Italian (I know, I was surprised too), but it's worth it for the pretty, not overcrowded beaches.