as of Feb. 2025, the methodology in the official documentation doesn't work.

I think it hasn't worked since the move to focal. But there is no one yet who has taken it upon themselves to update the documentation on that point.

Noting that, as of Feb. 2025, the methodology in the official documentation doesn't work.

Is there any inconvenience to calling 'apt remove <package>' directly with 'libertine-container-manager exec' or using a libertine shell e.g. lish?

Don't remember what lish does exactly, but you can achieve a command line that looks like a root shell with libertine-container-manager exec -c fakeroot. Then you can apt remove and / or install packages to your heart's content.