In addition to nifty.sh for UP as recommended, you might be interested in Conversations.im, an actively developed, well known XMPP client with mobile optimizations[1] to keep battery use low which can act as your UP broker (distributor) on the device. Note they talk about needing a proxy to convert message types at the bottom: https://unifiedpush.org/users/distributors/conversations/
[1] using two XEPs outlined on their site: https://conversations.im/#features -> Mobile optimizations
This is the tricky part - you will be remote-invisible until someone from the other instance(s) follow you for any of your content to show up in their Explore (hashtags, etc.) feed for other people to discover you. Pixelfed.social is the biggest hub by far so getting on that radar is key (much like joining a small Mastodon instance and you want to be "seen" on mastodon.social e.g. - same processes).
So you want to follow yourself from your pixelfed.social account to your own domain.com, so that your domain.com profile is seeded (federated) for other pixelfed.social users to discover as they browse. It's a hack but there's no other real way given how "opt-in" federation works, unless you have pre-existing friends on pixelfed.social who subscribe to your domain.com for you right away so you don't have to hack it to get started.