All brake fluid is the same with the exception of dot 5 because it is a silicone fluid.
Use whatever you like.
The difference is in a nut shell that the higher the dot # the higher the "quality" so use dot 4 or 5.1 or 3 or whatever you like. Adding any number to any different number does not do anything bad.
Now if you want to understand brake fluid the basic idea for the sake of a short post is that the higher the dot# the higher the boiling point is but this comes at a cost trade off of service to keep that wet boiling point.
Basically dot 3 will last a long time but it's quick to fade out vs 5.1.
Just 5% water in the system will turn the wet boiling point in half. It's a small system so just a tiny bit spoils the system. It's been proven that aluminum and cast iron brake calipers will leach moisture into the brake system due to the vapor intrusion during heat cycles.
If you want to have the highest dry boiling point then you trade off service. Basically some of not most 5.1s require fluid change every 6 months.
Just slap some motul 5.1 in there and change it once a year. This stuff is cheap and the highest performer on the market with the longest life.