5+ years ago I participate on a project who started a community from the ground up using a self-hosted https://discourse.org.

The experience was pretty great, the user experience in general is good, onboarding is straight forward, is mobile friendly, it has email and in-app notifications for replies, weekly digests and more. And you own the data!

Later down the road, a chat platform was necessary too, and we use Telegram channels for that. I remember considering some OSS/Self-Hosted options for that but Telegram was really easy and the trade-off was worth it.