You are going to be fine with your meeting!
Microsoft increased the meeting limit from 250 to the new limit of 1000 participants. All 1,000 participants will get the same experience such as chat, ability to show video, mute themselves, see the presentation, etc.
If you are participant 1,001 to 10,000 however you will still be able to join the meeting but that participant will experience a meeting where they can only see the presentation being shared. They will not be able to interact - so no reactions, no chat capability, and no ability to show their video.
It's all mentioned here: View-only meeting experience - Microsoft Teams | Microsoft Docs
and here: What’s New in Microsoft Teams: June 2021 - UC Today