Summary:
With the changes made in https://www.minecraft.net/article/minecraft-snapshot-20w30a, beds and respawn anchors avoid respawning you onto dangerous blocks, including magma blocks. However, this does not apply, if there are carpets or trapdoors placed above them.

Steps to reproduce:

1. Set your spawnpoint using a bed or respawn anchor

2. /gamerule doImmediateRespawn true

3. /kill

4. Replace the block you are standing on with a magma block

5. /kill

6. Place a carpet or trapdoor on top of the magma block.

7. /kill

Observed results:
You respawned on top the carpet or trapdoor despite it being on magma block, meaning you will take damage.

Expected results:
The game should avoid respawning you on carpets and trapdoors that are placed on top of magma blocks