The fixed height helps a bit by eliminating the reflow, but it still feels very sluggish.
To address we can add a fixed height to the template previews in table layout, and add a loading indicator which obscures the preview until fully loaded.
I tried solving it once in #61408, but it wasn't the ideal approach. let me remove myself from assignees as I can't think of any other solution at the moment.
Related: https://github.com/WordPress/gutenberg/pull/59792
Here's Table layout:
https://github.com/WordPress/gutenberg/assets/846565/4dca44f6-7436-44ad-b44a-bc171758b145
It feels very clunky how the templates load piecemeal. It's particularly bad in this layout due to the reflow that occurs when the templates load.
Here's Grid layout:
https://github.com/WordPress/gutenberg/assets/846565/97a565d5-f695-47aa-ae94-67546ca0b30b
The fixed height helps a bit by eliminating the reflow, but it still feels very sluggish.
To address we can add a fixed height to the template previews in table layout, and add a loading indicator which obscures the preview until fully loaded.