You should put the lemmy-ui’s port (8635) first then in the conditions blocks, the lemmy’s port

set $proxpass "http://0.0.0.0/:{{ lemmy_ui_port }}";
if ($http_accept = "application/activity+json") {
set $proxpass "http://0.0.0.0/:{{ lemmy_port }}";
}
if ($http_accept = "application/ld+json; profile=\"https://www.w3.org/ns/activitystreams/"") {
set $proxpass "http://0.0.0.0/:{{ lemmy_port }}";
}
proxy_pass $proxpass;

https://join-lemmy.org/docs/administration/troubleshooting.html

New lemmy’s instance here. Hello.
I come on your topic to test. Might as well enjoy of your topic.