Here’s what I have for Pleroma.

server {
server_name social.immibis.com; # this is what matches the domain name
root /var/www/social_html; # empty folder
location / {
proxy_pass http://localhost:4000;
}

# this block was from the pleroma documentation, I think. Mastodon and Lemmy might have their own recommendations. Upgrade is to enable proxying websockets. and the rest seems generally sensible for proxying.
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection “upgrade”;
proxy_set_header Host $http_host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
client_max_body_size 16m;
ignore_invalid_headers off;

# when you run Certbot it will change this to 443, insert SSL configuration, and set up a redirect on port 80
listen [::]:80;
listen 80;
}