Google Photos and Google Chrome gained support for viewing Ultra HDR images and recently Adobe Lightroom has also added support for editing ultra HDR images. Ultra HDR is a new image format available with Android 14 on supported devices & camera. Basically it's a JPEG image but some additional data added to it when captured on supported devices. With ultra HDR, images can have darker shadows and brighter highlights.
Google Messages is the newest app to take advantage of ultra HDR images and make the messaging experience a lot better for people who use RCS. Google quietly added support for Ultra HDR images back in September just before Pixel 8 series launch. Yupp, I went on an apk compilation spree to find that because I noticed the flag recently inside the apk. The flag is - bugle.support_ultra_hdr.
While I don't have a supported device to test if it really works, I asked a few people on telegram with Pixel 8/8Pro to test it. @spawnpointdes on telegram tested it and confirmed that it actually works. I just asked him to send an Ultra HDR picture using RCS to someone and tap on the sent image to check if it's showing as an ultra HDR photo. While there is no text or sign in the image preview screen to see if it's ultra HDR images, he mentioned that it works because when switching back and forth through recents screen, the image would be dim and then brightens up when the Google Messages's image preview screen is opened. A sudden brighting of the image is the sign of an HDR image.
There is one more thing, as Mishaal Rahaan mentioned in an AndroidPolice article, "many social media services compress images that you upload, which can corrupt or strip the HDR gain map from the metadata." The good news here is that Google Messages doesn't strip the gain map metadata from images. It strips some of the other metadata though. Images sent through Google Messages are usually compressed but even after compression, the gain map data will still be present in the sent images and it will be show as Ultra HDR in Google Photos.