I wonder what causes the crashes. Is it a buggy MTE implementation (or buggy hardware), or are app devs doing something that would only cause crashes under MTE? Maybe it’s something they are using like a library or framework?

Its buggy apps. Ive been using MTE for pretty much all the apps on my GrapheneOS phone for 3 years without any problems.

2 apps have C++ libraries and MTE makes these crash due to memeory bugs, so I disable MTE for these.