Here are some Blu Tack alternatives that don't leave marks. Hang things on your walls without worrying about marks with these products.
Forbidden Chewing gum strips (Blu Tack) : r/forbiddensnacks
Is There a Blu Tack Alternative That Doesn't Leave Marks?
Zero clue on how to erase these marks, anyone got any tips or tool
How To Remove Blu Tack Stains From Wall
What Can You Use as an Alternative to Borax?
Bostik Blu-Tack 75g - Stationery
What Can You Use as an Alternative to Borax?
What Can You Use as an Alternative to Borax?
2 Pack Bostik Blu Tack, Multipurpose Reusable Adhesive, Clean
What is Tack Cloth and How Do You Use It? - The Handyman's Daughter