Hi
when I have to upgrade to a new system, whether it is the operating system version, the Ardour version or directly the motherboard, the hard drive, etc., I do the following:
I check the projects and note down the plugins that are used, if not all of them, at least the most important ones.
I look for and copy the folders where the plugin files are and save them on a disk or USB memory stick.
Just in case, I save and copy configuration files, especially if, as in my case, I use my own configuration file for my midi controller, which is not included by default in Ardour, and also in my case the color theme of the Ardour interface that I modify for my needs.
Basically, you have to copy and save everything that is not there when you install Ardour again (plugins, midimaps, theme, etc.).
Even if all you do is install a new version of ardour without uninstalling the previous one, it is a good idea to save some of the files, in my case the theme, because with the latest versions of ardour when installing the new version without uninstalling the previous one, the new installation modifies the existing files, something that did not happen before.
If you copy the plugin folders and when you have the new system you copy them again and tell ardour to scan them, it does not matter so much that the folder is in the same place as in the old system.
The important thing is that the content of those folders is the same, that is, that you have the same plugins as before changing the system.
I use linux ubuntustudio and I copy the lv2, vst, vst3 folders from my home and apart from the other possible folders that are sometimes installed in different places from the home in linux.
As I also use some vst from windows I copy the ones I have in the wine directory.
Most plugins will work without any problems, although some may need to be reinstalled.
By doing this, I usually have no problems restarting projects.
Regards