Have exactly the same problem with same Bose Companion 5 speaker setup as mentioned by Ash after installing Windows 11 24H2 Build 26100.2161.
After a couple of minutes without any sound, the speakers are turned off.
This was working fine pre 24H2 update so it has definitely got to do with that, moreover since this problem exists with a lot of people as present in this thread.
Please fix this, since it is very frustrating to have to turn on speakers again and again and again....