I have mentioned F-Droid many times in the official Matrix before they moved to Discord and not been banned. You might be misunderstanding what actually happened or have not asked the moderators why someone was banned.

No one has been banned from our chat rooms for mentioning F-Droid. That's a completely fabricated claim easily disproven with a search. There are a massive number of discussions about it where people often disagree about it.

GrapheneOS has official chat rooms on Matrix and Discord to provide people with multiple options. We also have semi-official Telegram and SimpleX groups.