this seems to work after using google takeout to save a .mbox file with the messages:
I had to use --noresume because I previously used both -action restore-group --action restore-mbox
so at first attempt all emails where imported in the admin inbox
I also confirm the all messages can be imported in a normal mailbox, where I get errors about message size when importing to group:
Restoring from 91.17mb file c:\mbox\accou...@gmail.com.mbox...
message 8 - 51.85%
ERROR: Media larger than: 26214400 - Giving up.
message 9 - 100.00%
ERROR: Media larger than: 26214400 - Giving up.