I just installed the most recent iOS 18 beta and all the app icons that had been dark are now back to light mode colors. I turned off and back on dark mode. I restarted my phone. I really liked the look of the dark app icons so I’m very hopeful those will return upon the next update.
You should probably raise this as a bug in the usual way. It won't really get progressed if it's only posted in these Developer Forums.
You need to raise each issue you find separately at https://feedbackassistant.apple.com/ You can post the FB numbers here if you want, so that others can link to them.