in 1.21.2 and above, entity-sourced explosion whose causing entity is under water will not destroy block-like entities, including items, armor stand and decorations. However, such explosions under water still destoys item entities.
Environment
1.throw a netherite-like item under lava.
2. prime a tnt under lava.
3. the lava will destroy the item.
As of 25w20a, TnT once again destroys item entities when under water, thus resolving this report as invalid.