Liquid Glass Transparency Effects on macOS 27
These don’t really appear to work for me but jotting here anyway. (Cached from this post).

Softer scroll edge
# System-wide
defaults write -g MPV8 -bool false
# Per-app example: Mail
defaults write com.apple.mail MPV8 -bool false
# Restore system default
defaults delete -g MPV8
# Restore Mail default
defaults delete com.apple.mail MPV8
Fully transparent
# System-wide
defaults write -g NSScrollPocketEnabled -bool false
# Per-app example: Mail
defaults write com.apple.mail NSScrollPocketEnabled -bool false
# Restore system default
defaults delete -g NSScrollPocketEnabled
# Restore Mail default
defaults delete com.apple.mail NSScrollPocketEnabled
Restart affected apps, or reboot Mac.