[GistNoesis]

What I usually do is search mails according to specific criterion, put a label on all of them so that they are easily downloadable from https://takeout.google.com/settings/takeout (you can sub-select only the specified label there)

Then a few hours later I receive the download link and download them. Then search for the label and delete them all to release the space.

Don't use the existing archive functionality, because you won't be able to delete them all ; by doing a "in:archive" search the div which propose to really select them all won't pop-up (feature or dark-pattern I don't know).