.fbx – Converting blender 4.5 to 5x

There’s no such thing as 100% security. So in doubt, definitely keep a backup of your data before moving to 5.0.

We do not know exactly what your files are and what they contain. The only things we can know is the official information from Blender.

New Blender versions are made to not break data: changes to the data structure are intentionally rare and kept to a minimum, usually until an exceptional release where they group up the biggest changes. And when there are changes, the developers make sure it is handled instead of just left to break. E.g. if a node in v1 is removed in v2, the devs will make sure that v2 can open a v1 file and convert the non-existing node into the v2 one.
If there are known breakages or limitations to be aware of, they are announced on the version’s release notes, which you can find as a short and illustrated form on the main website, and as a longer and more documented form on the developers’ website. Most of the time, it’s going backwards in Blender versions that is risky, not forwards. But again, there’s no such thing as 100% security.

That being said!

Your question sounds awfully like a XY problem. You have an issue X, and you ask about solving another Y issue instead of tackling issue X.

If it’s an important or even professional project and you are not sure about what to do, I would advise to not jump versions during a project. You mention having problems importing or exporting FBXs, why do you think updating Blender and getting another version of MPFB would solve that? Maybe ask a new question to find a solution for your I/O issues instead.