The best elaborate magic system.

[Saiangeli]

I love the details and ideas of a detailed magic system. I like isekai alot but they rarely make a detailed and intricate magic system and focus on it.
Anything with a detailed skill and magic system and how they are used is what im looking for.
Preferably Male MC and romance is a huge plus.

 

[Wake-the-winds]

Might not fulfill the itch but I really like the magic system in Skeleton Soldier. It's not the most elaborate but it feels very cool and and natural. The way it gets developed gradually as the story goes is very satisfying so it's always at the front of my mind when I think "good magic system."
Witch Hat Atelier also has a super cool magic system, really enjoyed it. Absolutely ripped it off once or twice for DnD.
And uhhh, kiiiiiind of a magic system but Darwin's Game has some interesting shit going on with it. That manga is slightly trash, esp at the beginning but it ends up gradually getting real weird and I love that sort of shit so can't help but give it a passing mention.
@Saiangeli

 

[Tykora]

Try "Death March kara Hajimaru Isekai Kyousoukyoku"
It has romance, a male mc, and alot of over detailed systems mainly skills but they work like magic and he has to be creative with how he uses them