imapbackup

I use an IMAP backup program that runs on my own windows system. It backs up my mail from Google Mail and multiple IMAP accounts that I use for business, personal, and family purposes. Because it's a collection of files and folders, the PST format is portable and easy to back up.
You can use this tool on Windows, though you might need to install a free version of that tool.
Mozilla has a good summary of IMAP Backup Tools worth looking at.
https://www.shoviv.com/gmail-backup-tool.html
https://www.shoviv.com/blog/how-to-backup-imap-emails-from-imap-mail-account/