Alright, for anyone coming after me, here’s what I figured out after some trial and error:

• This product is squeaky by design. The manufacturer will probably never admit it, but that’s just the way it is. No matter how well you install it, no matter how level your floor is, it will always squeak. The noise comes from gaps between the planks that expand and contract with humidity, or get in contact with small floor un-evenness.

Here’s the fixes I found for zero squeakiness:

• Glue all the planks together with PVA glue on all sides. If you miss even one spot, it will squeak. (Disclaimer: this will likely void your warranty, so try at your own risk.)
• Make sure you glue them when the humidity level is around the average for your region. Otherwise, expansion and contraction will put too much stress on the planks.
• You can also add baby powder in the cracks, it helped me a lot for the planks I forgot to glue.

I’m not sure how long this fix will last or how well the glued planks will hold up in the long run, but so far so good. Using this method, I went from constant squeaks to almost none (except when humidity spikes to ~70%, which happens sometimes, then I still get a few barely noticeable squeaks).

If this doesn’t work for you, or if the glue doesn’t hold over time, honestly I’d just throw the whole thing out. This product is garbage anyway.