I want to start off by saying, I have no complaints about aoe4, have thoroughly enjoyed it and it was well worth my money, however I’m getting a bit over it and looking for some new game suggestions
Please finish my sentence! 
If you like age of empires 4, check out…
If you liked the historical immersion and want more realistic battles, check out the Total War series.
If you liked the building aspect and want more of that, check out the Anno Series.
If you expected more empire management, try Paradox Grand Strategy Games.
Everything else is rather old like the old Stronghold games, Knights of Honor, Battle for Middle Earth etc.
If you don’t mind the year; Command & Conquer Generals: Zero Hour
It should give you a similar experience to AoE4, in some ways, but with greater strategic variety.
Really nice games : Company of heroes 1-2, Iron Harvest, Rise of nations
Other interesting : Frost Punk, Northgard, Banished, Kingdoms and Castles, Spellforce 3
… age of empires II de.
It’s a dumb suggestion, apologies, you’re probably asking for something more different, but if IV was your very first experience with RTS or your first in the age franchise, it could be worth giving age II a look. It has a lot to offer both in single player and multiplayer. Not to mention exceptionally good campaigns, official and custom. Please forgive my useless response , good luck with your quest.
Most likely any other Age of…
Then, I think sc2 is still the most polished rts. Has a lot sp content and the coop stuff is also great. If you’re into MP, good luck though. It’s extremely fast and unforgiving and not as many new or mediocre players to mess around with. At least in matchmaking.
Then there is WC3, with the dreaded Reforge version. C&C and SC1 remaster, if you don’t mind some more archaic games and 2D graphics.
You could also check out the first Dawn of war + Extensions.
Depending on what you liked most about AoE4, there are other games that can be recommended.
theres a game on the app store called “rise of kingdoms” it is similar to this game however it is a live game… meaning you live in a world where its a kingdom and there are live events everyday etc. It’s more if a diplomatic, alliance game