17 Done today at 09:03 BST today at 09:03 BST Refresh all snaps: no updates
18 Done today at 09:24 BST today at 09:25 BST Install "core18" snap
19 Done today at 09:25 BST today at 09:25 BST Refresh all snaps: no updates
20 Done today at 10:23 BST today at 10:25 BST Install "hello-world" snap
21 Done today at 10:33 BST today at 10:35 BST Install "snapd" snap
Hmm it’s possible that the core snap was not installed before, but since it’s required by hello-world, it got pulled in. Can you attach the output of snap change 20?
pi@raspberrypi:~ $ snap change 20
Status Spawn Ready Summary
Done today at 10:23 BST today at 10:23 BST Ensure prerequisites for "hello-world" are available
Done today at 10:23 BST today at 10:25 BST Download snap "hello-world" (29) from channel "stable"
Done today at 10:23 BST today at 10:25 BST Fetch and check assertions for snap "hello-world" (29)
Done today at 10:23 BST today at 10:25 BST Mount snap "hello-world" (29)
Done today at 10:23 BST today at 10:25 BST Copy snap "hello-world" data
Done today at 10:23 BST today at 10:25 BST Setup snap "hello-world" (29) security profiles
Done today at 10:23 BST today at 10:25 BST Make snap "hello-world" (29) available to the system
Done today at 10:23 BST today at 10:25 BST Automatically connect eligible plugs and slots of snap "hello-world"
Done today at 10:23 BST today at 10:25 BST Set automatic aliases for snap "hello-world"
Done today at 10:23 BST today at 10:25 BST Setup snap "hello-world" aliases
Done today at 10:23 BST today at 10:25 BST Run install hook of "hello-world" snap if present
Done today at 10:23 BST today at 10:25 BST Start snap "hello-world" (29) services
Done today at 10:23 BST today at 10:25 BST Run configure hook of "hello-world" snap if present
Done today at 10:23 BST today at 10:23 BST Ensure prerequisites for "core" are available
Done today at 10:23 BST today at 10:24 BST Download snap "core" (11191) from channel "stable"
Done today at 10:23 BST today at 10:24 BST Fetch and check assertions for snap "core" (11191)
Done today at 10:23 BST today at 10:24 BST Mount snap "core" (11191)
Done today at 10:23 BST today at 10:24 BST Copy snap "core" data
Done today at 10:23 BST today at 10:24 BST Setup snap "core" (11191) security profiles
Done today at 10:23 BST today at 10:24 BST Make snap "core" (11191) available to the system
Done today at 10:23 BST today at 10:25 BST Automatically connect eligible plugs and slots of snap "core"
Done today at 10:23 BST today at 10:25 BST Set automatic aliases for snap "core"
Done today at 10:23 BST today at 10:25 BST Setup snap "core" aliases
Done today at 10:23 BST today at 10:25 BST Run install hook of "core" snap if present
Done today at 10:23 BST today at 10:25 BST Start snap "core" (11191) services
Done today at 10:23 BST today at 10:25 BST Run configure hook of "core" snap if present
......................................................................
Make snap "core" (11191) available to the system
2021-06-28T10:24:58+01:00 INFO Requested daemon restart.
......................................................................
Automatically connect eligible plugs and slots of snap "core"
2021-06-28T10:24:59+01:00 INFO Waiting for restart...
Yup, loooks like it. So core got pulled in, which means that snapd no reexecs from core, and you have a new version (2.51). That unblocked installation of the snapd snap, which the old version would complain about, but the new version isn’t so picky.
you’d have installed it in that process … and normally snapd also complains that it can not find a base when you try to run a snap and do not have core installed … also installing the first snap from the store usually installs the required base alongside … perhaps 2.37 did not have that feature though …
just link to the doc though also note that there are many other OSes you can use on a pi and that there are more than just pi based arm devices someone might run your snap on …
Nobody likes to read long docs (even me ), and most of the users will use Raspbian on Raspberry PI. So it worth just add one more line to my “Getting started”, maybe with small note with above link somewhere very deep inside footer