On the LAN Turtle, AutoSSH is running:
root@turtle:~# ps
[…]
28771 root 936 S /usr/sbin/autossh -M 20000 -i /root/.ssh/id_rsa -N -T -R xxxxx:localhost:22 turtle@vps.domain.tld -p 22
[…]
root@turtle:~#
(Debian man page about autossh [https://manpages.debian.org/bullseye/autossh/autossh.1.en.html] is not complete enough to understand all the command line arguments.)
From here, everything looks ok. No problem with the ssh connection to the VPS.