Does anyone know best practice or if the forum supports uploading a GMS2 project or zip file to attach to a forum post. I have multiple projects I want to share and write up a tutorial page for but some of them are too complex to use code brackets for every single thing.
I don't believe you can upload anything but images to the GMC (others should correct me if I'm wrong).
Many tutorial authors use free file hosting services, and then post the link. There are many good sites available -- just avoid sites that require your viewers to create an account to get the download.
Regardless, posting some critical section of code
in the tutorial topic is a good idea. This gives members (and moderators) some idea of the complexity (and quality) of the tutorial without having to download a file.