This bug was probably already fixed. As long as the Fire Protection total adds up to 7 or higher (for example, a IV and a III) you should not get any fire on your screen. You still take lava damage as normal, just slightly reduced because it is Fire Protection. This means that you should not catch fire with a full set of Fire Protection 2 but should get fire with just a chestplate with Fire Protection 4, which is how it currently works in 1.16.20
Slow falling works on a horse as long as you are not riding it. The bug is that slow falling does not work on a horse while being ridden. This is similar to the bug where jump boost also does not work on a horse while being ridden.
This also affects mobs wearing elytras. The player with the cape needs to be wearing an elytra for the same elytra design to show on other players/mobs, but the design won't go away on other players/mobs if the player with the cape removes their elytra. The bug is still in 1.16.0.
I think the Continuous Block Breaking System should be enabled in survival mode because it allows for some very interesting mining techniques and is useful for when you want to break a weak floating block that you would otherwise need to stack up to, such as the top of a tree. Also please make sure this bug fix does not slow down creative mining speed, as I and many others find it very useful to be able to mine 2-tall tunnels at sprint-flight speed with the correct angle.