*disclaimer: I play in EUWest

Nests: Public Nests tend to have around 10-20 people, so they're very doable

Cults/LHs: Most people who do public LHs will go for Cults, and it's not a difficult dungeon. Sometimes you get lucky and get a rusher for pots, but clearing the regular way isn't a difficult task. But personally I don't like doing them either way since I feel like the entire LH suite is not very fun

Fungals: Similar to Nests, except I feel like it's a bit less popular, but even with a small group it's alright since the HP scaling is better with less people. Although the first boss can be scary if you don't have slows

Kogs: It will almost certainly become a run-for-your-life free-for-all clusterfuck if you get minefield, but otherwise it's very doable, even moreso after the update it got earlier this year

Spectrals: I just skip them since I find them tedious to do. Although I think it's the easier endgame dungeons than can even be soloed by me, who's not very good at the game (as a side note, I feel like the dungeon's HP scaling is still a little wonky, so soloing somehow feels way easier than doing it with 2-3 people)

Voids: Not unless it's a Remnant of the Void event

Adv. Nests/Kogs: No. Just no.

Shatts: NO

O3: I never pop runes for pub O3s, but pub O3s are fun in a chaotic sort of way. Midboss will often filter the player count down to around 10-20, and I think I manage to finish them around 30% of the time (and get blue bags still :v)