Showing User-Selectable Themes

[merefield (Robert)]

Are you simply looking for this?:

Hamburger Theme Selector

This theme component currently only works with the Legacy sidebar setting, which is going to be discontinued. Please see Sidebar theme toggle as an alternative. Summary Hamburger Theme Selector adds a theme selector in the hamburger menu provided there is more than 1 user selectable theme. This selector works with both logged-on users and anonymous users. Repository Link https://github.com/discourse/discourse-hamburger-theme-selector …

By default users can select the Theme they would like within their Preferences, but that’s less convenient.

Note the Admins can determine if a Theme is User selectable or not.