Updated PL5 this week and can’t send Lightroom classic files there.
Also PL% browser also does not work.
??? if you’re referring to photo library as browser - that’s working here (OS 11.6)
I am Os Monterey
I “am” running Monterey on my 16inch MacBook pro
The “???” were because I don’t know what you meant with “PL% browser”? But looking at the keyboard, “PL5” would be the closest guess? I don’t use LR, but Monterey (I’m better used to 12, I need better things to remember than Apple’s guesswork “is Mojave newer than Big Sur)” 
) is the latest, so I would not expect everything to run as it should be. Too many companies are involved with far too many goals, and ⅔ of them are not famous for rapid troubleshooting. The new MacBook Pro doesn’t let much of a choice.
Can’t help with the LR issue as I only use LR CC at the minute and I don’t believe the option to send to PL exists in CC. I certainly can’t see it if it is supposed to be there anyway. So could indeed be a bug there?!
Again though, if by browser you mean the Library then also working fine here with latest version of PL5 and also MacOS Monterey.
What exactly are you finding doesn’t work with the browser/library?
IIRC you have to give PL permission to open folders the first time you attempt to use that directory under MacOS.
Have you inadvertently declined thy permission?
I believe I understand the issue. As I am on the latest version of the MAC OS, Photolab 5 and latest version of Lightroom Classic.
I too can not send files from Lightroom to Photolab via the plug-in. Currently my work around is to drag a photo from Lightroom to Photolab. Then export from Photolab to Lightroom. The Photolab to Lightroom export part works still.
Greetings,
If correct permissions have been "allowed’ in System Preferences > Security, maybe opening a ticket with support is in order.
Providing the versions of all installed applications PL and Lr, the steps to reproduce and possibly log files if any information was captured will be helpful.