Reduced colour depth after upgrade from Adobe Photoshop Element 2018 to 2026

I don't know of any setting or other solution that may be applicable.  I suggest you contact Adobe Support and see if they are aware of this.  You can start a chat session by going to the Contact Adobe Support page. (https://helpx.adobe.com/contact.html?rghtup=autoOpen) Make sure you are signed into your Adobe account and try typing Agent when the chat window opens in order to avoid the chatbot. (If you use my link, the chat window should open automatically.)

While I can see some differences between your two screenshots, that doesn't tell us very much.  The two images as uploaded are different dimensions.  So has one been edited and the other not?  Are the original images raw or jpeg or something else?  Has any editing been performed on the images before the screenshot was taken?  Are the images being viewed on the same monitor?