I was able to fix this, but only switching to Edge (was using Chrome), reloading the page, typing gibberish in the boxes, selecting the proper category for the feedback, and then pasting my feedback made it work.
can confirm this affects 1.19.4 full release
the bug doesn't seem to be lava aquifers, but rather all caves being filled with lava at -56 and below
changing the lava_level in the cave carver doesn't work, the game just ignores it outright and sets it to -56 (default is "above_bottom": 8, which is equivalent to -56 on normal worlds, hence why nobody noticed)
the following didn't work: (i tried a lot of things trying to fix this)
-disabling aquifers (it just made EVERY cave an aquifer, somehow. this also caused water to generate above lava if a cave intersected -55, turning the lava to obsidian all at once when updated)
-disabling lava aquifers by setting "lava" to -1 (nothing changed)
-changing "lava_level" in cave carver to "absolute": "-2000", slightly above the minimum height of my world (again, the game seemingly ignores this field)
-changing aquifer generation settings all to -1 (aquifers above -56 no longer generate, but at -56 it's still lava)
-changing lava lakes to generate water instead of lava (nothing changed except presumably the actual lava lakes)
One of your friends may have their profanity filter on and/or have their Microsoft account's age set to below 18.