It’s not as easy as to “just import” some armature or bones made in some other application with some importer converting it into blenders armatures and then export it with some other export to convert it to that bones. There might eb some knowledge needed; for example about special needed or not root bones etc…
So you might have to learn about all the features of the importer and the exporter as well and and also how to do some possible “fixes” in blender after importing or before exporting… so “simply” trying to restart or re-install will not help you at all.
I actually got it working perfectly without any extra complicated steps in the end. I simply imported the PMX and exported it as VRM. It wasn’t difficult at all. Thanks replying.