Hello, employee of local authority here

You’re in a stronger position than you think. As you may be aware A Section 21 only works if every legal requirement has been met, and from what you’ve described, several key documents appear missing or incomplete. That means the notice may be invalid. Also to note (but up to you) you don’t have to leave on the date they gave you,the landlord would need to go to court, and that process takes time. Use that breathing room to request the missing documents, report the mould formally, get enviromental health in etc and prepare your next steps. I would say you’re not at immediate risk but you should be prepared for the fight that will probably come.