In Subnautica 2, equipping two Strike Armor modules to your Tadpole submarine grants 100% damage reduction, making you completely immune to all creature attacks including the Collector Leviathan.
How to Become Invincible Step-by-Step
Step 1: Travel to the Alien Research Outpost
Head to the Southern Mercury area — it’s very close to the Southern Mercury base. Travel along until you see the Alien Research Outpost at the middle of your cursor on the map.

Step 2: Find the Strike Armor Module
At the Alien Research Outpost, locate and scan the Strike Armor module blueprint. This module gives you 50% damage reduction against creature attacks.

Step 3: Craft Two Strike Armor Modules
Take the Strike Armor blueprint back to your base and craft two Strike Armor modules at the Modification Station. You need both modules to reach 100% damage reduction. Funny enough, these two modules actually add together to give you the full 100% immunity.
Step 4: Install Both Modules on Your Tadpole
Open your Tadpole’s modification menu.

And install both Strike Armor modules on the same vehicle.

This stacking exploits a bug in the current Early Access build that allows multiple impact protection mods.
Step 5: Test Your Invincibility Against Collector Leviathan
Take your upgraded Tadpole to encounter the Collector Leviathan. You’ll see full armor integrity with zero damage taken no matter what the Collector does. You can literally laugh in its face and flash bang it all you want — it won’t be able to do anything to you.

Important Limitations & Warnings
Bonus: How to Scan the Collector Leviathan Safely
If you want to scan the Collector Leviathan while invincible, equip a bio modifier that turns you invisible. This lets you scan safely while the Collector Leviathan continuously attacks your Tadpole but can’t do anything against you.
The Strike Armor module is designed to give 50% damage reduction normally, but the game’s damage calculation adds both modules together instead of capping at 50%. This mathematical quirk gives you complete immunity to creature attacks. This lets you explore without worrying about the Collector Leviathan.
Even though you’re indestructible against creatures, remember that going below 450m will still cause damage from pressure, but you can use the repair tool to fix that easily.