Before you even bother going to the dev site to log in, have you contributed anything to the Garry’s Mod workshop before June 2021? If not, there’s no point continuing to read this thread. Otherwise, continue.
Firstly, try to log in to the dev site Login - s&box . Most likely the login wont be successful, however you’ll be shown a queue placing and an estimated time of when you’ll be able to log in. This is based on a workshop score.
The more successful your Garry’s Mod workshop uploads, the higher your score will be. Say you’ve uploaded 1 addon to the workshop and it has 100,000 downloads, chances are you’ll be near the top of the queue, however if you’ve uploaded 10 addons and they’ve got 3 downloads, you’ll be at the bottom. Its very simple.
(Note, even if you are number 3 in the queue, it can still take a day or two for you to get to the top)
Once you’ve finally and successfully logged in to the dev site, you will now have full access to S&box, just check your steam library and it will be there waiting for you in all its glory. Thank you for reading.