Windows: Creating transparent sticky notes in Windows using Notezilla - YouTube
Creating sticky notes with transparent background in Windows, using Notezilla – Conceptworld's Blog
7 Sticky Notes - Screenshots - Fun, interactive, powerful and cool Sticky Notes for your Desktop!
Also as dark, eg Dark Theme Desktop Notes!
Download free Transparent Note for macOS
Customized Tabs Flags Fluorescent Set Pet Index Transparent Removable Desktop Square Sticky Notes - China Sticky Note, Gift Sticky Note | Made-in-China.com