#deltachat is made to be a reliable and resilient messenger for private groups, friends and family.
If you want to use it for joining or creating "public groups", please do yourself a favor, and create a dedicated "public profile" by tapping "create profile" and then use it to join public invite links like here on the fediverse, or on websites etc
Public groups with anonymous un-trusted or trolling members can cause problems. Worst case, you can then drop the public chat profile.