I can confirm that updating po4a to the bookworm version (0.66) works. This is on both AARCH64 and AMD64. Here's how I did it:
Add a file to /etc/apt/sources.list.d called bookworm.list
Put the following in that file:
deb
deb.debian.org/debian
bookworm main contrib non-free
deb
security.debian.org/debian-security
bookworm-security main contrib non-free
deb
deb.debian.org/debian
bookworm-updates main contrib non-free
Create a file in /etc/apt/apt.conf.d/ called 99bookworm
Put the following in that file:
APT::Default-Release "bullseye";
Then I ran apt update. Finally:
apt -t bookworm install po4a
