First, look at the fish:
The letters upon them clearly spell out the word 'COCONUTS'. This is a prompt for us to examine the coconuts on and around the tree.
When we look at the coconuts we notice that:
Each coconut is 6x6 pixels in size, with a single white pixel within it. It is crucial to note that if we label the pixel in the top-left corner of the 6x6 grid as 'A' and proceed along the rows with subsequent letters of the alphabet, the positions of the white pixels spell out the letters 'C, O, C, O, N, U, T and S', as a nice self-confirmatory hint:
This is a hint as to what should be done with the fish - we need to overlay a similar 6x6 grid of letters on their internal shapes, which are also 6x6 pixel grids.
While I was able to suss which pixels are important within these without it, there is a visual hint provided by the OP as to what to do next - the sun:
The sun is a common pictorial representation of the Fibonacci sequence. The sequence here is:
1 orange - 1 green - 2 purple - 3 red - 5 grey - 8 brown - 13 blue - 21 yellow
So, to return to the fish, what we need to notice is that:
In each fish there is one colour which is used only once. And - would you look at that - reading the fish from top-left along the rows, that odd-pixel-out always corresponds to the equivalently-positioned colour in the Fibonacci sequence above! i.e. In the first box, the odd-pixel-out is orange, in the next it's green, then purple, red, grey, brown, blue, and finally yellow - exactly as per the sun hint provided by the OP.
We can then translate these:
Using the same decoding method as hinted via the coconuts. Interpreting these pixels using the 6x6 letter grid yields the letters: ZERO@ICA, where '@' here represents the 27th pixel in the grid, which is obviously beyond the normal scope of our 26-letter English alphabet...
So how do we fill the other boxes in order to make sense of the 27th position? A slight nudge from the OP in comments led me to realise that with 10 spaces remaining, it is highly likely these should be filled with the digits 0-9. This means our fish code yields:
Note here that the positioning of the fish bottom-left is important - as per the first clue...
...it is in a subscript position, slightly lower than the others..
This helps us answer the rebus. Because what we are looking at here is:
'sub nought' (the subscript '0'), the letters 'ICA', all of it below the word 'ZERO'. In other words, the OP has mainly been playing:
Subnautica: Below Zero, the open-world survival action-adventure game!
Got there at last! So it turns out the 19-pixel high seaweed strands which produced some Morse code gibberish are purely coincidental - d'oh!