Access chat in Microsoft Teams after meeting
Those chats are stored in the storage bucket belonging to the tenant that paid to host the meeting. As a guest to the meeting it’s up to the persons configuring teams server-side whether you get to participate in chat past the meeting time or just for the duration of the meeting.
I’ve found the in app help to be excellent, but we pay a lot for O365 and I believe our requests go into a priority queue. I would still recommend even free accounts try the help in app, nevertheless for this situation.
Your app is the same as everyone’s. Just like Office apps on macOS, it’s the same app for everyone, but the license you bring to it enables features based on which license Microsoft sees for your app/account. All you may need to do is pay more for your teams license if you need extra features.
In the paid version, the meeting chat is stored in the calendar, so as Microsoft adds features to the free tier, be sure to check in the calendar tab for past chats in case you do have access to them now or later.