itch.io

If anybody needs a walkthrough, here it is:
With timestamps for each progression item

There are timestamps for each secret in the description:

There are timestamps for each secret item in the description:

Yes

There's a secret island with a pretty tough bullet hell game there

If you've opened the "non-working" button in the puzzle behind the painting,
look at the sequence of pictograms on the wall above the aquarium.

Is there a way to win?

Like, the final boss seems a bit too unbeatable.