It could be fun to do some multi-day/mini arcs while still maintaining 4-koma format. As for ideas and inspiration, are you hoping to maintain the mix of dark humor, gag comedy, and cuteness? Personally I love wry humor and sex jokes, but plenty of sources and memes to mine material...
Meta/format parodies: You've already done isekai, so what about other genres and themes like a "in 100 days" series, otome villainess, or specific harem (e.g. 5toubon)? Expectation subverting gag comedy like Gokushufudou? Put Kyuu-chan in place of your favorite shota/loli from another series? Even Among Us fits pretty well with the tone of this series
Food and cooking parodies: Iron Chef? Manga-wise, we have Dungeon Meshi, Shinya Shokudou/Midnight Diner, Shokugeki no Souma, Wakako-zake
Horror/Dark/Edgy: You did Madoka. How about Junji Ito, Monster, Gantz, Youjo Senki, NGE, Wata-Mote, Fate
Cute: Jahy, Yurucamp, Yotsuba, Maoujou de Oyasumi, Ghibli films (e.g. Kiki's Delivery Service, Spirited Away - No Face or opening sequence with parents becoming pigs)
Companion/Pet: Natsume Yuujinchou, Spice and Wolf, Senko-san
Classic: "Oldies" but worth thinking about. FMA, Fruits Basket, or maybe classic stories/fairy tales like The Spider's Thread. I do love the literary references in earlier chapters, something nice about high brow-low brow humor. Or perhaps cinema or plays/musicals?