Bug Description

Some time ago i developed a small simple website with gutenberg & generatepress. i tried to use as many default blocks as possible.
Now i tried the performance plugin to support the great initiative to move to webp as also other platforms are doing the same as shopify and wix...

webps are generated correctly which i checked based on this request: https://wordpress.slack.com/archives/C02KGN5K076/p1649596392220539?thread_ts=1648893985.315499&cid=C02KGN5K076

It though seems that still the regular jpg images get used instead of the webp version of the images. see here:

Steps to reproduce

1. Upload jpeg images - implement them as background images or regular images in gutenberg blocks
2. install performance plugin, activate webp
3. use Regenerate Thumbnails plugin to generate the webp
4. See on frontend if they got used

Additional Context

• PHP Version: 8.0
• OS: Windows
• Browser: MS Edge
• Plugin Version: RC1