It’s best to think of the tanking scripts as “archetypes” instead of only relevant for a very specific fight.
The Mythic+ script is good for situations where you getting hit by multiple enemies often, and mostly physical/melee damage.
The Fallen Avatar script is good for physical-heavy single raid bosses where you don’t get much of a break (e.g. aggramar is pretty similar).
Felhounds is a pretty magic-heavy fight that ramps up and down in damage. It should produce similar gear recommendations to the Krosus script.
I haven’t looked at the Portal Keeper script that closely (that and Felhounds were made for us by another theorycrafter), but it could be a good “standard” physical heavy tank script where you have significant downtime between stretches where you have to tank.
For all of the scripts, you can increase the Mythic+ Level under More Options until it is at a level that is threatening for your character. e.g. Fallen Avatar is tuned for ToS heroic players, so you’ll want to jack up the damage to make it relevant for Antorus heroic players (from +8 to +10 is about the right level to make that script equivalent to a heroic Antorus boss).
If you are at 0% death chance even with the script tuned to the level you play at – e.g. heroic if you are mainly raiding heroic – that’s just fine, it means you are more than tough enough. You would want to focus on increasing your DPS instead. The Blender in the gear optimizer should help you out with that: if you are using the heroic raid boss gearing strategy and the Conservative blend option, once you are really tough, it will start pushing you towards DPS gear even though it is trying to be “conservative” – you just don’t need more toughness.