Yes, you can leave a meeting without any problems.

Tap on "More" at the top right of the meeting and then on "Leave meeting". You do not have to give a reason. Only from 8 hours before the meeting is a reason required, which is then displayed to the other participants in the chat - so the other users know even if you cancel at short notice.

Once you have left the meeting, you automatically leave the group chat and can no longer access the messages.

However, be fair and try to actually come to the meetings you have agreed to!