(banned person could be reading this thread)

Banning is a governance issue for any community. If the community is large enough, there may be other senior (by time and participation) community members willing to act in a leadership role. Ask for their help in formalizing the ban process.

The governance group (ideally excluding you) can engage the currently banned person in a public process on the forum, where terms of engagement are defined by the community, not lawyers or countries or emotional individuals.

If the costs (time, money, risk) of maintaining a forum become too high, other admins have closed their forum. Presumably the aggrieved party simply wants to participate in the forum, not destroy it.