Magnetic connectors work well in this case, and you won’t need that tape. But if you move your keyboard around a lot they might be a slightly worse solution than yours ;-)

I haven’t done it myself, but I’ve seen videos - you’ll need to de-solder the existing port (or whatever is left of it) and solder on a new one.

I’m not sure where ConnectBot stores its keys, so I can’t help with the ‘transferring to termux’ part :-)

What I can tell you is that you should be able to generate and use SSH keys directly in Termux. Here’s a quick guide on how to do it: https://gist.github.com/evandrocoan/f503188587587d7b1d1ba8746c9c6107

I’ve switched phones recently, and I haven’t set up my keys yet, but as far as I recall I went through a similar process a few years ago to set up SSH keys on my phone (I haven’t tried the steps in that article myself).