Tarantula hunting, Turnips, etc. I found going to islands and gathering all the fruit and selling them (if they're not ur native fruit) can give you quite a bit. You could also sell assessed fossils if you don't care too much about the museum
I’ve been trying to farm sharks but it seems as though they’ve made it more time-consuming due to auto-save. I usually run into them around 5pm/6pm onwards. I find myself going in and out of buildings helps to speed things up.
Haven’t run into Tarantula’s myself but I’m in the Southern Hemisphere.
I had iron garden chairs be the item of the day, so i made 50 of them and sold thrm for 224k total. I'm out of iron nuggets now though, but with the huge amount of island tours I take, that won't be an issue. But yeah, sonetimes the hot item of the day might help. But I like its such a hard grind because it feels awesome I get to pay off another part of the house.
For me personally, I've just been farming ocean critters. It's about 7k~12k a pop but occasionally I'll get lucky and catch an oarfish. I recommend looking online for what fish and bugs are worth what.
I noticed hermit crabs are now 1k, emperor butterflies (the big blue ones) are 4k, the paper-whatever butterflies (bigger white ones) are also 1k, and football fish are 2.5k. Red snapper are also worth a few k as well.
Of course, going to islands helps. Finding a tarantula island could get a loan payed quick. Rare fruit also could spawn. One of the islands I went to had a tendency to spawn sturgeon at a much-quicker rate as well.