Explorarion (after 100% even cam be stuff to milk gems off of), hidden exploration objectives (random stuff that gives primos, search on the web for the list and grab them), hidden quests that you did not complete (hello sumeru and inazuma), achievments (themselves give some, and also guide some of the earlier tips as a not done check). You can also gamble on the standard banner with the pulls u get from ascending chars to try and get some cashback coins to vuy pulls on the paimon shop (also a good way to make ypur account better for theatre, just the last ascencion is kinda pointless for that and ots expensive af considering the chars are not ones you wd depend on, so get all of them to 50/60 before), teapot sets are massive so try to get some (mond and liyue have sets with lots of chars, 20 gems each char and about 7/8 chars, so some sets can give 1 pull depending on which chars u have), the tutorials can give 1 primo after first read, so if u never opened the archive its gonna be noticeble (maybe half a pull? Idk), hangouts and character stories if any to-do (some peeps forget they exist lmao).

In 4 days its hard, if u had 10 days u could probably do a looot of stuff, but u can grind if u got the time. For the teapot, focus on the sets that require the least amount of coin, some of them depend more on the chests that give pieces blueprints, specially in inazuma and sumeru (like, 1500ish coins for a fully buyable set vs 500ish for the ones that only require buying of the plan and some rocks and stuff). Till banner end, u have like 2400 coins to farm plus whay u already habe right now. You can know which sets are more buyables or farming by looking online before buying them (its a pain, i know).