Because you are running macOS 27.0, first install any available macOS 27 update before troubleshooting further.
Apple has introduced changes to Liquid Glass in macOS 27, including a control that adjusts its appearance from ultra-clear to fully tinted. Apple — What's new in macOS 27 Golden Gate
For the Apple Account avatar, change the photo through iCloud.com and then reopen System Settings.
Apple states that the Apple Account photo changed through iCloud.com should appear on devices using that account. Apple — Change your Apple Account photo on iCloud.com
If it disappears again, record the steps and result.
For the Liquid Glass issues, go to System Settings > Accessibility > Display and ensure Reduce Transparency and Increase Contrast are off.
Then test the Liquid Glass setting again.
Apple describes this control as changing the appearance from ultra-clear to fully tinted, so a change in perceived darkness as it moves toward the tinted setting is consistent with its documented operation. Apple — What's new in macOS 27 Golden Gate
Check whether the black or uneven borders remain in Spotlight, Dock labels, Finder menus and other interface elements.
If they do, capture a screenshot or short screen recording. Test the same behaviour in Safe Mode as well. How to use safe mode on your Mac
For the delayed Liquid Glass changes, change the setting and see whether the affected interface updates immediately, after switching applications, or only after reopening it. Repeat the test after restarting the Mac.
For the customized screenshot folder, create another customized Desktop folder and manually add a file to it.
Compare that with a screenshot being saved automatically to the original folder. This can establish whether the behaviour is specific to automatically saved screenshots.
For the fullscreen close or minimize delay, test several applications, including an Apple application.
You can also temporarily enable Reduce Motion under System Settings > Accessibility > Display and see whether the behaviour changes.
For the brightness and volume overlay, reproduce the effect with text underneath it and then temporarily enable Reduce Transparency.
If the appearance changes, note the result and capture a short screen recording if possible.
One additional useful test is to create a temporary standard macOS user account in System Settings > Users & Groups and test the affected features there.
If the same problems occur in the new account, that provides useful evidence that they are not limited to your existing user environment.
If they occur only in your original account, the next troubleshooting step would be different.
I would not reset preferences, delete Finder preference files, use Terminal commands, reinstall macOS, or erase the Mac at this stage.
First complete these controlled tests and compare the results.
When reporting the remaining problems to Apple, include MacBook Air 13-inch, macOS 27.0, Dark Mode, the affected features, the steps that reproduce each problem, and the fact that you did not observe these behaviours on macOS 26.6.2. Screenshots or short screen recordings should be included for the visual problems.
If you believe you have identified behaviour in macOS 27 Golden Gate that does not function as intended or does not appear to work as described in Apple’s documentation, you may wish to report it to Apple as a possible software issue.
Apple can review the report and determine whether the behaviour requires further investigation. To help with that investigation, it is important to provide clear and accurate steps showing how the issue occurred, what you expected to happen, and what actually happened. Apple may also request additional information, diagnostic logs, files, screenshots, screen recordings, or further steps to reproduce the issue.
If Apple decides that the report warrants further investigation, the issue may be examined by the appropriate Apple teams. Those investigating the issue may attempt to reproduce the behaviour under controlled test conditions and determine whether it occurs consistently and whether the reported steps reliably produce the same result.
If the behaviour can be investigated and is determined not to be working as intended, Apple may identify a potential fix or take other appropriate action. However, Apple may also determine that the behaviour works as designed, that additional information is required to diagnose the issue, or that the issue is caused by third-party software or hardware.
For this reason, a clear and repeatable set of steps, together with relevant diagnostic information, is one of the most important parts of an effective report to Apple.
Apple's published guidance specifically recommends providing detailed reproduction steps, expected and actual results, and relevant diagnostic information. Apple also notes that it may request additional information or files while investigating a report. (Apple Developer)
