So I can archive all my emails 2008 → 2022 in EagleFiler and remove folders under /Users//Library/Mail/ ?
I can see that Mail is duplicate my archived emails, and now Mail folder (/Users//Library/Mail/ ) is over 22Gb.
If I save EagleFiler library in iCloud folder I can access my old emails also via iPhone?
I archived my mail, one year at a time, so there is changes only once in year.
Yes. However, I recommend deleting the e-mails from within Mail rather than modifying the folders directly. Normally, there should only be one Mail/V# folder, because when you update to a new version of macOS it migrates the previous Mail data to the new format. For example, Ventura is V10.
The files will be available in iCloud Drive, however iOS does not have built-in support for displaying e-mail files. Normally, EagleFiler stores one large file per mailbox, for efficiency, although you can also store e-mails as individual .eml files in a folder. These are standard file formats, but I don’t have a lot of experience with which iOS apps know how to read them. It looks like EML Viewer Pro can handle .eml files in iCloud Drive. There are probably others.