Brucehankins Just as a matter of habit, I always set up multiple drives with their own boot partition and keep systems completely isolated.
I refuse to use a shared boot partition anymore. Sooner or later, single-partition dual booting always tangles the bootloaders and requires a new installation. Like you, I set up my drives so that each has its own boot partition and is completely isolated.
I run two almost identical micro desktop computers, both dual-boot, dual-drive, dual-boot-partition. On the 7080, W11 is the default boot, Solus the secondary boot; on the 7070, Solus is the default boot, W10 the secondary boot (so I can help my geezer friends with W10 as needed).
I keep the W11 computer and a Solus computer side-by-side, working with both during the day. Both have been remarkably stable, with no issues whatsoever, for a long time. I frankly wonder why the norm is to try to dual boot from a single partition.
WetGeek I decided about a decade ago that dual-booting was never going to be an answer for me, so I have very little recent experience with it. To be more accurate, I have NONE. Installing a secondary OS in a VM is far more satisfactory, in my opinion, and that's what has worked well for me.
I use Gnome Boxes to check out various disros on my Solus computer. I haven't noticed a performance issue, but I can devote 8GB/40GB to the distro installed in the box, which is more than adequate, and Gnome Boxes seems to be resource light in comparison to VMware and VirtualBox. I won't use Grub for a bare-metal installation on any computer, period.
Enough said, I guess. It doesn't look like any of us are in a position to offer much useful help to @Kuka with installing W11/Solus on dual drives using a single boot partition. Luckily, though, there are several threads on the issue that he can explore.