The bug
If you set the gamerule fire damage to false, you still get damage from magma blocks. This also was a bug on java edition and got fixed. MC-160919
How to reproduce:
Run this command: /gamerule firedamage false
Place a magma block
Make fire somewhere
Go into survival mode
Go into fire
✔ You don’t take damage from it
Go on top of the magma block
❌ You still take damage from it.
Affects 1.16.200.51