Please highlight on that image what you are meaning is “impossible”. Multiple Disk Sets have always displayed fine for me. Don’t often go over ten disks so it is harder to say what happens there.
I do have a weird combination of scripts in place as can be see by the two Edit Relationships tabs at the top.
If this is just about the open or closed list views - notice how I opened this one CD manually by clicking on the purple arrow, and the second CD is still closed (as can be seen by the direction of that purple arrow)
Comically only CD11 is the one I have linked to Works so far. And you can see that shows a more normal layout (I think?)
And this has been working like this all week.
My copy of Vivaldi has these scripts on that page. I can get settings from them (but you’ll need to tell me where to find those settings on a PC - I assume stashed in %APPDATA%\Vivaldi somewhere?)
To be honest with you, I don’t know what half of them do. I have added some and then forgotten when they are doing or why. Just know how unusable the default MB website is for me without these additions.