One of the issues with waterproofing Tetrinsic are the LEDs. They're COB, yet still only IP20 rated, and I can't find anything that has a higher rating with similar features and formfactor. So I turned to searching for a DIY solution and found this:

The video can be summarised by this image found on LinkedIn:

To get IP65, the strip has been coated with heat shrink tubing. This tubing exists on AliExpress and sounds like it'll turn a 2.7mm LED strip into a 4.3mm one:

In regards to the PCB, it's probably possible to use shrinkwrap here too as it looks like its what the industry does:

On the other hand, another idea was from the comment section of the below video:

A commenter suggested to use mineral oil. This seems like a nice idea since I'd be able to confirm an airtight seal before this touches water, and the oil will prevent the enclosure from being crushed by water pressure. I then wondered if the MEMS microphone would be ok, but a hacker has actually used mineral oil specifically to make an underwater microphone:

[Jul 13] I'm thinking of using the same M2 pin (as used by the gears) to terminate the side of the LED strip that doesn't have wires connecting to it. I'd need to use multi-core wire so that the adhesive seal works on that side too.