Hi, I tried to move my KMail data to a new computer. The KMail client got bugged and now it creates hundreds of Unnamed identities on every start of the client. I don't know how to do a clean install of the client, the identities still remain saved no matter what I do.
I tried to export my data once again before trying to reinstall the client but now I can't even import it again because there is allegedly "too many local folders".

I don't know if this description helps a lot. I just want to know how to do a clean install of KMail client. It is really frustrating not to be able to move my e-mail between computers. (I haven't been using the client for that long either)

https://ibb.co/rGHR5FL

I can't help you solve this, but I can add my voice to complain about the pathetically sorry state of Kontact/Kmail's migration tool. This last weekend, I too tried to migrage my mail over to a new hard drive. I only got 3 mysterious (numbered) identities after trying to restore a 3.2GB backup file. None of my account settings were restored and none of my mail. The process took long enough but it was an abject failure. The disturbing thing is that as I start to research this, I see that people have been complaining about Kmail/Kontact's inability to back itself up in a restoreable format for years. If I dig into the Zip file that was created, I can find the individual messages. Seriously, why can't we just copy a folder tree from drive to another and be done with it? Or at least create a tool that works reliably, but people have been complaining about this for years.