Turns out this issue is already fixed in the 6.4.4-3~bpo12+1 version available in bookworm-backports \o/
- Bug#1051367: Acknowledgement (regression: powersave screen ... Marcin Owsiany
- Bug#1051367: Acknowledgement (regression: powersave sc... Marcin Owsiany
- Bug#1051367: Acknowledgement (regression: powersav... Marcin Owsiany