On the Gimp-Forum.net website:
https://www.gimp-forum.net/Thread-Migra ... -Gimp-2-10
user nerudaj [Jakub Neruda] shared a link to his plugins:
https://github.com/nerudaj/gimp-pixel-a ... on-preview
I find it the most interesting: animation-preview with flexible, scalable GTK-based preview.

Playback for Gimp 2 does not support layer groups, so this plugin is used to preview animations stored in a layer group.
It allows you to have multiple animations within a single Gimp project, each stored in a separate layer group
(only the top-level layer groups are indexed for animations, so you can use layer groups at lower levels to perform blending operations).

Animations are played in reverse order to maintain consistent behavior with GIF exports in Gimp.
This means that the first layer in a layer group (=animation clip) is the last frame of the animation.

I've added a few minor changes to the plugin:
- include the current Gimp theme,
- specify the plugin's GUI start size [in line 150 you can change it (currently 700 x 800)],
- make the save as webp window open in the foreground,
- change the preview size increment [ - / + ] from 100% to 10%,
- change the menu location [ original location:Tools/Pixel Art/Animation Preview ]
to: Filters ➤ Animation ➤ Playback Group Layer...