Note that to do https fetches WordPress implements a copy of the Mozilla CA list.
I think this can be closed because Matomo already does try to use HTTPS when supported on the server-side. See https://github.com/matomo-org/matomo/blob/2ac2bc1aeaf8efce6bb9af92506311da99e1757f/plugins/Marketplace/config/config.php#L8-L16
I believe this has been now been resolved by PR https://github.com/matomo-org/matomo/pull/19098