Thunderbird on Linux? There are a number of solutions:
https://openrepos.net/content/accumulator/syncevolution
for instance. But this is missing a newer release. I’m adding it to the list of things to be aarch64’d
EDIT: I think it was @nephros that pointed out:
devel-su -p vcardconverter -e contacts.vcf
or
devel-su -p vcardconverter --export contacts.vcf
and
Calendar: devel-su -p icalconverter export calendar.ics
with the last being ical export. That’s somthing you could just push (pull ssh) …
Ah, it was @peterleinchen