The double # makes the object setting validation fail in the core (not this TC per se).
bad URI(is not URI?): "https://matrix.to/#/#matrix-meta-chat:fedoraproject.org" (URI::InvalidURIError)
It’s not strictly a valid URI, so you’d need to encode the fragment.
Here; using https://matrix.to/#/%23matrix-meta-chat:fedoraproject.org will work.
Looking at the code:
is_valid_url is defined here:
You can see they already have another function to deal with this situation and is being used in other places:
I think it’s reasonable to use relaxed_parse for the theme object URL validation.
E.g.: if validations&.dig(:url) && !UrlHelper.relaxed_parse?(value)