1.16 set the precedent that some items are immune to being melted by lava (in other words, are immune to its effects). Some items in the game currently would also seemingly fall into this category, but don't. These are:

• Armor enchanted with Fire Protection
• Blaze rods (Blazes are immune to fire and lava)
• Blaze powder
• Magma cream
• Netherite scrap

And, although a bit more up to interpretation:

• Obsidian, crying obsidian
• Fire charge