I wasn't too concerned about it but now I have time to tackle this problem that has been there since the beginning.
Thumbnails are displayed correctly on the desktop website, but on mobile they are sometimes too large so that the layout does not look correct as in attachment. Is there a way to display these in the correct format? I use the WebP generator but even without it I have the same problem.

It looks like size of your images is not same across listings.
Do you use force image aspect?

Force image is used

@mwindey
Then such output is expected.

@Mb Themes,

There is no difference in using force image aspect, the problem persists with any setting on/off and gets even worse if i activate the webP plugin and use it for thumbnails.

Well you must regenerate thumbnails then and clean browser cache.

Weirdest thing is that when i disable webP plugin....Enable force image aspect and regenerate images everything is perfect.
Enable webP plugin / upload image and the image is not sized correctly. Also regenerate after activating webP plugin the image sizes are not correct no matter if force image is on / off.

@mwindey
Plugin create copies of jpg/png variants in webp format.
If that variant is created with force image aspect, then sizes will be different.
Browser & hosting cache comes into count as well to properly purge old cache and really look on newly created images.