Export/Migration/Update

Hello, colleagues.
There is an ancient (the engine and plugins are updated, just many years of all this) installation of WPMU with sites on subdomains (some subdomain sites of the network with their domains), as well as with BuddyPress. During the operation, a certain number of errors and conflicting scripts have accumulated, when correcting which the thought arises that it might be more rational to demolish everything and re-install it (the network is mostly cleaned up and only a small amount of valuable content remains).
Hence the question: if this is really more practical, then what tools are known for the most “seamless” export/import of users (I would like them not to have to re-register (especially in their own blogs) and no unnecessary notifications were sent to them), content and basic settings? BuddyPress can be donated. I suspect that I want to restart the database right away, because I can no longer adequately identify all the garbage left over from old plugins, etc.