We recorded a demo back in 2021/2022 with Mixbus, version unknown. Maybe 7 or 8.
Unfortunately there is no way to get Mixbus back without buying it.
Is there an easy way of importing a mixbus project into the latest version of Ardour?
Or is it the only way, to open it and delete all the mixbus related plugins and reroute every track?
I work with Linux and I have Ardour and a Mixbus 10 version (I won’t switch to 11 given Mixbus’ commercial policy)
I think the only solution when you have a mixbus project is to simply open the project with ardour. I just tested it and it works…
… However, all the routing will have to be redone (especially with the buses) and all the specific Mixbus plugins will be grayed out (obviously all Mixbus channel strips are proprietary to Mixbus and cannot be loaded in Ardour.
So you can get your project back but the mix will have to be redone…
…i think.
Hm, that’s unfortunate.
I am curious: What happened to V11? It was always more commercial IMO.
I think it’s off topic and that, perhaps, the administrators of Ardour would not like us to discuss criticism on Mixbus here. I refer you to the Mixbus forum, especially on the new Mixbus licensing system
Yes, and you likely also have to add inputs to the master-bus: click on the master bus input connector > add audio port (because In mixbus busses and master are only fed by sends).
Thanks, Robin. 
Maybe, there is a way to automate this in some way.
Is it all in this one project-XML?
You could write a Lua script.
Yes it is.
Maybe, there is a way to automate this in some way.
Dunno how complex your session is, but you might get to a useful result sooner by opening a fresh session in Ardour and importing the audio / MIDI from the interchange folders of the Mixbus project, and then rebuild the routing in Ardour without needing to work around the missing Mixbus signal chain.
Whether you start from an empty Ardour session or open the Mixbus session in Ardour, doing the fixups by hand at least once would be essential before trying to script it: if you only have the one session, then there is no win.
Not that complex.
I found an old MBv8 installer link in a forum, so I can use the demo to export the stems, then start with clean projects.
If you are exporting, and would like to start “fresh”, then I would recommend disabling channel processing (plugins, the MB compressor and EQ, etc.). See this page in the Mixbus 8 docs.