lupdate of Qt 6.1 does not support Python but in Qt 6.2 that problem no longer exists so you have 2 options:

Install Qt 6.2 and use its lupdate.
Wait for PySide6 6.2.0 to be released (at this moment it is only available for windows) and use lupdate.
I have a python project written with PySide2 and now I want to migrate to PySide6. I used Qt Linguist to translate UI and created .ts files with help of this command:
pylupdate5 utility from PyQt5 package (but it worked fine for my project with PySide2). Now I plan to get rid of PySide2 and PyQt5 packages.
So, I need to replace pylupdate5 with something from PySide6 package. I assumed lupdate should to the job but it seems it works only with C++ code. It gives me errors like Unterminated C++ character or Unbalanced opening parenthesis in C++ code. An with lupdate -help I don't see how I may switch it to python mode (similar to uic -g python).
Does anyone know how to create .ts files for Qt Linguist from python source files?
How to create .ts files for Qt Linguist with PySide6?