Hello DenverGrandDad,
Thank you for participating in the Apple Support Communities! We understand that when viewed on other devices, iCloud Photos are showing in lower resolution than expected. We'd be happy to help point you towards a resolution.
The first step is to ensure that the other devices you're viewing these photos on meet the requirements shown in the resource below, as it can impact the quality of your photos:
Using HEIF or HEVC media on Apple devices - Apple Support
Next, check if there's an improvement on the quality if you download one of the photos following the steps here:
Download iCloud photos and videos - Apple Support
Keep us posted on the results.
Cheers!