This plugin isn’t necessary with the Air Theme (because it already shows the preview for the topic), for example, but is necessary with Mint theme.
I’d like to have a selector for which themes this plugin will be enabled. Is it possible?
In Customize goto Component. look through the components listed there. There will be a component installed with Air Theme giving you the preview.
In the Air theme it looks like your looking for Topic Thumbnails.
This one is similar and has other features when combined with a plugin(be sure to verify plugin is still actively developed if you want to use Sidecar)…
It’s a Pavilion Plugin. It is.
To clarify – because you specifically asked about a Plugin – AFAIK it is not possible to selectively (per Theme) enable a Plugin.
However, Theme Components can be selectively enabled per Theme.