See the screenshot for what went wrong. What can I do here?
Try to update the template of your dom0 update proxy qube, then update dom0 and restart the system.
After this try to install the qubes-dist-upgrade package again.
Update of whonix-gw-16 template failed
sudo qubesctl --show-output --skip-dom0 --templates --target=whonix-gw-16 state.sls update.qubes-vm
whonix-gw-16:
ID: update
Function: pkg.uptodate
Result: False
Comment: E: Release file for tor+https://deb.whonix.org/dists/bullseye/InRelease is expired (invalid since 68d 17h 29min 47s). Updates for this repository will not be applied.
Started: 07:46:22.812409
Duration: 16704.894 ms
Changes:
ID: notify-updates
Function: cmd.run
Name: /usr/lib/qubes/upgrades-status-notify
Result: False
Comment: Command "/usr/lib/qubes/upgrades-status-notify" run
Started: 07:46:39.519359
Duration: 5692.826 ms
Changes:
----------
pid:
1835
retcode:
100
stderr:
stdout:
Summary for whonix-gw-16
Succeeded: 0 (changed=1)
Failed: 2
Total states run: 2
Total run time: 22.398 s
Install Whonix 17 templates (gateway+workstation) and use them instead of your old Whonix 16 templates.
You can use Qubes Template Manager GUI tool for this or qvm-template command in dom0 terminal.
Thx, installation worked.
Running the upgrade updating the whonix-gw-16 and whonix-ws-16 failed for the same reason.
Can I go on with all stages and fix this manually the same way after the in place upgrade finished?
Upgrade process stopped after stage 1. 
Just remove Whonix 16 templates so they won’t cause the issues, you won’t need them anymore.
Retry upgrade after removing the templates.
Just remove them, or remove them after I did the manual update for whonix-ws-16 too?
Oh, I overlooked, that you already told me to install both.