Hi,

I can confirm in a pure environment:

1. guix shell --pure minetest le-certs -- minetest
2. click on the +
3. In the GUI: ‘No packages could be retrieved’.
   In the terminal:

   2022-01-22 13:19:05: ERROR[Main]:
https://content.minetest.net/api/packages/?type=mod&type=game&type=txp&protocol_version=39&engine_version=5.4.1&hide=nonfree&hide=desktop_default
not found (SSL peer certificate or SSH remote key was not OK) (response
code 0)

Minetest uses curl HTTPS, so as a fix, I tried adding

    (native-search-paths
     (package-native-search-paths curl))

to the package definition of minetest, such that SSL_CERT_FILE/DIR
would be set.

To test:

1. apply the patch (see attachement)
2. ./pre-guix shell --pure minetest le-certs -- minetest
3. click on the +
4. In the GUI, a list of downloadable mods is shown.

The first patch contains the actual fix, the later patches do some
‘cleaning’.  I'll sent a mail later confirming that the later patches
don't break Minetest (assuming that's actually the case).

Greetings,
Maxime.