Installed Win 11 on my PC this weekend alongside Ubuntu, Win 10 and Manjaro and all four are working fine. MSI motherboard set to Legacy+UEFI boot. I didn't do any special tricks to get around TPM (which I had enabled); I've not verified if the TPM2.0 is active or not, but I assume it is (albeit potentially being undermined by legacy being active). Using Manjaro Grub as my boot menu, although on the occasions I do boot into Windows I do then have to go through the Windows boot selector (10 or 11).
Perhaps I've done something egregious with my boot-time security, but I figure it's probably no worse than it was previously, it just might be no better.
Hope this gives some confidence to others, albeit your mileage may vary.