I play in a "match-the-stack" house game that regularly gets very deep and very multiway. I have a solid understanding of approximate GTO pre-flop play in 100-200BB games, but feeling uncertain about 300-500BB games where implied odds go through the rough, and my loose aggressive AND passive opponents can often get away with calling super light.

Any advice on how to shift my strategy? I haven't ponied up for a solver/classes and my in research, deepstack theory is usually 150-200BB.

Basically u wanna make the nuts.

So big pairs are nice to overset smaller pairs.
AXs is nice to overflush
Big connected cards are nice to over straight little straight.

So I want hands like TT+, AKs-A2s, and KQ-T9 for strong straight.
I don’t want baby pairs 55-22, I don’t want Q9s J9s, or 78s

That makes sense and is more or less how I've adjusted.

It feels like I'm playing much more passive, waiting/calling for the nuts or draws to the nuts. And much less like beating my opponents over the head with high pairs/kickers or high EQ draws.

Is it just my imagination that super deepstack is more passive nut roulette? Is it actually more interesting because of the SPR?

My fellow players believe we should be opening much wider pre-flop since "anything can be the nuts" and when the blinds are so low relative to the stacks, "it's basically free to see the flop." However, this feels off to me and so I've kept it fairly tight. But without the TPTK kind of pots. Feels like I'm waiting for the nut-over-nut lottery.

I think u can play ur nut draws much more aggressively rather than passively. So then u can be doing a lot more semi bluffing towards the nuts.
U can raise nut draws deep because even if u get reraised u can still call and u have deep stacks for implied odds.
Then to balance that out u do still need to raise some strong made hands and strong vulnerable hands as well.