Not sure you can directly play most games let alone steam/civ games on ipad due to their restrictive nature, you will 100% not be able to play mods i know that much, you may be better off getting an android tablet which is less restrictive, cheaper and probably better but i don't know if steam or civ runs on that.
That said steam have a new handheld console called a steam deck which is just a linux based pc in a handheld system and a very powerful one at that, think the 64gb retails at $399 and most people get that then upgrade the ssd themselves to 1tb etc...
And i do know you can run linux, steam os, windows 10-11 and other os too on the steam deck so the worlds your oyster on that machine
