Import a HUGE Gmail mailbox in Apple Mail

One of our managers has a huge Gmail mailbox, ~400GB. They started it when it was more human-sized, managed with Apple Mail. Growing over time wasn't apparently a problem for a 2021 MBP with 32GB of RAM. Now they had to change the computer and we didn't have the chance to migrate the profile on the new device, so we had to start a new sync from scratch. This proved to be a nightmare! Gmail is enforcing an IMAP hourly (or daily) data transfer limit of ~1.5GB. This makes it impossible to feed Mail from IMAP directly. We did a Google Takeout of the mailbox, and we now have this multi-Gigabyte Mbox file. Trying to import it in Mail hangs it, reaching ~95GB of consumed RAM (out of the 48 physically available). So I was wondering if there's some other way to load this file directly in Mail without passing through the import. Maybe placing the file (original or converted) into Mail data dir, and letting it reindex later. If this is not possible, is there any other way to work with this Mbox file? thanks