This is a development release of the code using new dependencies and betterproto instead of google's terrible python implementation (it's legitimately awful). It's possible this is broken, i haven't been able to really test it.
Install instructions are the same for previous versions. For brevity/laziness i didn't copy them here
This code has a breaking change in the database that stores your credentials. you must delete it before using the latest version Fixed in the latest, by @don-de-marco
You can find it at C:\ProgramData\GOG.com\Galaxy\storage\plugins\steam_<gibberish>.db on Windows, and at /Users/Shared/GOG.com/Galaxy/storage/plugins/steam_<whatever>.db on MacOS.
Update: 21:20:48 UTC Thursday, June 8, 2023 Replaced release with newer, hopefully not broken version
Update: 18:40:51 UTC Friday, June 9, 2023 Fixed the infinite recursion error. added a bunch of type-hints (not breaking) and renamed a bunch of variables that used reserved an/or namespace keywords (possibly breaking if i missed a few).
Update 21:30:00 UTC Friday, June 9, 2023 Removed last vestige of Google's Protobufs i could find in the code. The hint was pretty useless anyway, am now using the proper better proto form.
Update: 00:20:06 UTC Saturday, June 10, 2023 Removed a bad clear from protobuf. updated the install order. fixed an issue with black (a code styler)
Update: 00:35:00 UTC Saturday, June 10, 2023 Re-implemented the fix from 21:30. was somehow lost.
Update: 02:35:00 UTC Saturday, June 10, 2023 Fixed some reference issues (apparently TYPE_CHECKING was not good enough). Fixed the enciphered password so it was the right type.
Update: 21:09:37 UTC Saturday, June 10, 2023 Largely fixed by @don-de-marco . Removes last traces of protobuf, added new type hints, some better type coercion for fixed64 proto values (aka floats in Python, these should be ints most of the time). Fixed a bunch of bugs i made.