The other day, I wrote an articleshown below, and I was thinking about whether I could prepare or have a machine that can run the server continuously.
NostrP2P: Pure P2P Distributed Microblogging System - ryo_grid's tech articles
Then, I remembered that there is an app called Termux that creates a unique Linux environment within an Android device. So, I thought it would be a good idea to use an old Android smartphone to run the server, and when I tried it, it worked perfectly!
(The idea behind Termux is that since Android is a type of Linux, by changing the root location of the file system in the shell shown to the user with chroot and placing the necessary files, you can create a unique Linux userland.)
First, referring to the sites below, install Termux via the Fdroid app.