@ViridityCorn Yes, you're quite right. I see now what my mistake was. I was looking for a "search communities/magazines" function, which does not yet exist in Artemis (unless I've missed that too).
Browsing All, then clicking on a magazine name you're not currently subscribed to, and then the plus button on the top right does subscribe you to that magazine. It didn't occur to me to do it that way because I never use All, I browse only magazines I'm subscribed to, even on using kbin's website. So in order to join a new magazine, I was looking for the Artemis equivalent of this search screen: https://kbin.social/magazines