So then the only theoretical limit on black hole mass would just be how fast you can put matter in black holes and/or merge existing black holes versus how fast the universe expands?
I'm 100% an armchair physician so take my words with a grain of salt but it seems like according to the math there is no limit to how massive a black hole can get. There are limits on the size of how big and small things can get and how hot or cold they can get, the second part is pretty cool, Physics Explained on yt has a good video on it (he's got a lot of good videos) but I enjoyed this one on what the maximum temperature is in the universe: https://www.youtube.com/watch?v=NVlEQlz6n1k
I heard a joke about a nerd who dies and finds himself in a very hot underground cavern. The devil is there, and says "Welcome to Hell! This over here is the lake of molten lava where you'll spend the rest of eternity". The nerd says "well actually, since it's underground it's called magma rather than lava". The devil replies, "um, you do understand why you're here, don't you?".
I try to remember that when I'm tempted to point out mistakes that are fine to overlook.
