Earlier this year before I knew client-side image processing was coming to WordPress 7.1, I created a free and open source WordPress plugin called Menagerie. It originally converted any image upload to AVIF or WebP in the browser, then uploaded saving some server bandwidth. So, pretty much what WordPress core can do now. This is always painful when you make a plugin and months later it's in core. Oh well.

Not all is lost though! Menagerie is still very useful. I stripped out what Core now does and left/enhanced the parts that Core doesn't automatically do. Core doesn't automatically ensure every upload converts to AVIF or WebP. Menagerie steps in to make sure that happens, gives you a JPEG fallback image, ensures your images are wrapped in <picture>, and provides a bulk image converter for your existing images. Plus, has a nice little toast message to confirm if the conversion was successful or not.

Tools within Performance Lab are another option. But, those are all server side I believe? And, a lot... Look at all those plugins that the Performance Lab page lists. Is all of that necessary? Depends on the situation and who you ask I suppose.

TL;DR

• Not Menagerie: WordPress 7.1+ processes your images in the browser when possible and then uploads
• Menagerie forces AVIF or WebP conversions; Still WordPress 7.1+ doing it in the browser when possible, but Menagerie is telling it to go with AVIF or WebP based on settings
• Menagerie creates your JPEG fallback for when a WebP or AVIF image can't be displayed
• Menagerie wraps images where possible in <picture>
• Menagerie gives you Open Graph image settings
• Menagerie lets you quickly convert all existing images

See also: https://wilcosky.com/my-quest-for-image-sanity/