XMPP is best for that IMHO.
You know that even Synapse is not following the specs? Basically the specs follow Synapse, often with a huge time lag.
Conduit has been hit by that many times when they tried to follow the specs, just to realize they are outdated and incompatible with Synapse.
Good time to switch to XMPP 😅
Technically it is possible, and I have heard rumors about some eastern European providers given unique public IPs on request, but practically no, not possible/available.
Basically a VPN where the endpoint is a VPS or a specialized service that offers a public IP.
For public services you will need some kind of tunnel, as cellular networks or Starlink will not provide you with a public IP. Otherwise no big issue with an ARM SBC and a somewhat decent battery.
The base consumer models from regular brands usually have no write cache and are thus cheaper, and obviously slower, but for data storage that doesn't matter so much.
But you can also look into 2.5" HDDs if you are looking for power savings and noise reduction over regular HDDs.
Well, obviously if you host from your home ISP, people will be able to figure out your home's approximate location via a reverse IP search.
But otherwise go for it. It's not that hard to do and a nice learning experience.
Something like that could be also interesting for a Lemmy frontend to make it easier to share images on instances that have strict upload limits.
Wait for the next hardware upgrade and then set up a new system while keeing the old system running in parallel.
It requires a bunch of browser features that non-user browsers don't have, and the proof-of-work part is like the least relevant piece in this that only gets invoked once a week or so to generate a unique cookie.
I sometimes have the feeling that as soon as some crypto-currency related features are mentioned people shut off part of their brain. Either because they hate crypto-currencies or because crypto-currency scammers have trained them to only look at some technical implementation details and fail to see the larger picture that they are being scammed.
I find Cheogram and Monocles to be good looking and featureful clients, so not sure what exactly you mean. They are certainly not any worse than WhatsApp, Threema or Signal in that regard.
On iOS I agree though... Monal is not bad per se, but it needs some work on the UI side of things.