In the changelog it says

• Mining speed and blast resistance of creaking hearts is doubled

However, creaking hearts take longer time to mine in snapshot than in 1.21.3.

Steps to reproduce:

1. Create a world in 1.21.3 and place down 4 creaking hearts.
2. Give yourself 2 netherite axe with Efficiency 18 and 17 respectively.
3. Run /tick rate 1.
4. Mine a creaking heart with these axes. Both axes should mine instantly.
5. Open the world in 24w46a. Run /tick rate 1.
6. Mine the rest creaking hearts.
7. (x)Note you cannot mine instantly with Efficiency 17 one, but Efficiency 18 is fine.