It's been a while since I've updated the bare-metal (Ubuntu) server installation, which is still running on 8.2.7 using an external MySQL database without problems. I've followed the upgrade guide: https://docs.onedev.io/upgrade-guide/bare-metal, but I can't upgrade, I get the following error:

/opt % sudo /opt/onedev-9.7.0/bin/upgrade.sh /opt/onedev
Running OneDev Upgrade...
--> Wrapper Started as Console
Java Service Wrapper Standard Edition 64-bit 3.5.51
  Copyright (C) 1999-2022 Tanuki Software, Ltd. All Rights Reserved.
    http://wrapper.tanukisoftware.com
  Licensed to OneDev for Service Wrapping

Launching a JVM...
WrapperManager: Initializing...
default THREAD FACTORY
INFO  - Launching application from '/opt/onedev-9.7.0'...
INFO  - Cleaning temp directory...
INFO  - Starting application...
INFO  - Upgrading /opt/onedev...
ERROR - >>> Error: Could not find or load main class com.gitplex.commons.bootstrap.Bootstrap
ERROR - >>> Caused by: java.lang.ClassNotFoundException: com.gitplex.commons.bootstrap.Bootstrap
ERROR - Unable to upgrade specified installation due to above error
INFO  - Stopping application...
<-- Wrapper Stopped

This probably is because the versions lie too far apart. I'd hoped to install some late 8.X.X version or early 9.X.X version as an intermediate upgrade step, but the oldest still available build is 9.2.0, which gives the same error:

/opt % sudo /opt/onedev-9.2.0/bin/upgrade.sh /opt/onedev
Running OneDev Upgrade...
--> Wrapper Started as Console
Java Service Wrapper Standard Edition 64-bit 3.5.51
  Copyright (C) 1999-2022 Tanuki Software, Ltd. All Rights Reserved.
    http://wrapper.tanukisoftware.com
  Licensed to OneDev for Service Wrapping

Launching a JVM...
WrapperManager: Initializing...
INFO  - Launching application from '/opt/onedev-9.2.0'...
INFO  - Cleaning temp directory...
INFO  - Starting application...
INFO  - Upgrading /opt/onedev...
ERROR - >>> Error: Could not find or load main class com.gitplex.commons.bootstrap.Bootstrap
ERROR - >>> Caused by: java.lang.ClassNotFoundException: com.gitplex.commons.bootstrap.Bootstrap
ERROR - Unable to upgrade specified installation due to above error
INFO  - Stopping application...
<-- Wrapper Stopped

The 9.7.0 service installs fine, but cannot start because of the data version mismatch.

...
21:35:11 INFO  i.onedev.commons.bootstrap.Bootstrap - Launching application from '/opt/onedev-9.7.0'...
21:35:11 INFO  i.onedev.commons.bootstrap.Bootstrap - Cleaning temp directory...
21:35:12 INFO  io.onedev.commons.loader.AppLoader - Starting application...
TERM trapped.  Shutting down.
21:35:28 ERROR i.onedev.commons.bootstrap.Bootstrap - Error booting application
io.onedev.commons.utils.ExplicitException: Data version mismatch (app data version: 152, db data version: 122)
...

How best to tackle this problem? Making a backup of the data on the old version and trying to import/restore that backup in the newer version using restore-db.sh gives the same data version mismatch error. Do I need older builds to run multiple upgrades using in-between versions? And if so, where to get them since https://code.onedev.io/onedev/server/~builds does not show older builds than 9.2.0. Thank you for you time!

FYI: these are the /opt folder contents:

total 24K
drwxr-xr-x  6 root   root   4.0K Jan 24 21:40 .
drwxr-xr-x 19 root   root   4.0K Jan 29  2023 ..
drwxr-xr-x 13 onedev onedev 4.0K Jan 24 21:40 onedev              // active installation (8.2.7)
drwxr-xr-x 12 onedev onedev 4.0K Jan 24 22:03 onedev-10.0.0
drwxr-xr-x 13 onedev onedev 4.0K Jan 24 21:03 onedev-8.2.7
drwxr-xr-x 12 onedev onedev 4.0K Jan 24 21:03 onedev-9.2.0
drwxr-xr-x 13 onedev onedev 4.0K Jan 24 21:24 onedev-9.7.0