When you’re creating your topology data set, check the rules to make sure they can be part of the topology. Also, I’ve seen that if you have multiple data sets participating in topology, then sometimes there are issues.

I’d suggest simplify with just creating one topology data set with a single feature class. If that works, try adding one more with a simple rule. Finally, if that works, try again to add more feature classes with more topology rules.

Start off small, then add more complexity… If that makes sense. When you do this, you find the root of the problem of where the topology error is happening