I did inplace upgrade a few years ago on Windows Server running Veeam and it worked, but it's always recommended a clean install if possible. 

You can use the configuration backup to restore Veeam database after a clean installation. 

Clean install is preferred, but in-place upgrade should work. Just keep the PC-name the same, otherwise you have manual work with DB configuration

As noted it will work but migration to a server OS is the better way forward here as it is supported on Win10/11 but not recommended.  As noted have a configuration backup and if you can remove/reinstall it would be better.

Don’t in-place upgrade at all, there are risks and you might run into OS issues before even deepdiving into Veeam.

I agree with Chris, VBR should be running on a Windows Server OS.

Hi ​@ropi-ask, it depends! If you are using VBR solely on the server, I recommend a clean installation. But you may want to take a look at a this response from Veeam Support for more information: https://community.spiceworks.com/t/server-2022-inplace-upgrade-w-veeam-b-r-installed/963970/4

Keep in mind they are doing Win10 to Win11 not a Server OS but this would still pertain to any upgrade.  Switching to Server OS is still the better option.

I do agree in all points from my colleagues mentioned above 

But one additional point: It’s also an option, to check if your Inplace Upgrade (even if i wouldn’t recommend it) will work - and this is more regards to a general Option you have with VBR:

• do a Sure Backup from your physical VBR server (so you need an Agent Backup.. and also with a DNS server in this isolated Virtual Lab environment).
• if your VBR is running fine in this Virtual Lab, do your Inplace Upgrade there, check if it’s working, without any issues. If yes, you should be good to go for production.
• keep in mind, you wouldn’t have connections to physical other Repositories, Proxy and stuff like that - but it’s an indicator, if your Upgrade will work.