It really depends on what you want to use it for. Answers could be anything from a mini pc to an esp32

Take the handlebars off the bike?

You can write a luks key to a usb stick and use that to automatically decrypt at boot. https://wiki.nixos.org/wiki/Full_Disk_Encryption#Unattended_Boot_via_USB

It is its own program but sounds like maybe it was included in the packages that got installed when you installed sway

Maybe mako? if so "exec mako" would be in your sway config