I would vote for "certain locations". In general I find little reason to fast travel in BG3 - I go to the location, do the content, and mostly not return there. I think in the overworld I don't mind there being fast traveling (though I wish there was at least some attempt to explain it) but being able to just teleport out of the middle of goblin fortress or underdark completely kills any atmosphere those locations have. If you are telling a story of a brazen attack on an enemy stronghold, and delving deep into dangerous caves, then no, you shouldn't be able to just disappear.

Honestly, I think requiring players to reach teleporting spots would already solve this problem at least in EA content. See Elden Ring - blocking fasttravel at times can be a very compelling and memorable experience. I am pretty sure Larian did it themselves in D:OS2 in acr2 during Voidwoken ambush.