I’ve been obsessing over Perpollo recently, so I am legally and morally obligated to recommend any and all of that (especially Percy in Ancient Greece Perpollo or Percy in modern times as a med student/nurse/musician Perpollo or Percy struggling with his view of himself after Annabeth’s reaction to Akhlys Perpollo or Percy as Camp Mom Perpollo or mortal outsider pov Perpollo). I also really enjoy a lot of the Athenide AU and enjoyed some of the Broken Pantheon AU and Seer!Percy.
If you like longer stories and time travel I have to recommend ’Once more, slightly to the left’ by RosenMaiden which is absolutely AmAZing and is still being updated (though that does mean it is incomplete, it is updated fairly regularly). I would also recommend the ‘Nothing is Ever Set in Stone’ series by fanamaniac and ‘I have swallowed my pride (To say goodbye)’ by IzzyMRDB. The ‘A Family Built on the Weary’ series by DustShattersLikeGkass is also really good.