All the achievements are to complete puzzles so to get 100% just complete 300 puzzles.
You might think you have to buy all the DLCs and complete unique puzzles for this to progress.
But no, you can just complete the same puzzle 300 times.
I suggest doing a normal 20 piece jigsaw on the first image you can.
When you get into the puzzle screen press 4 then 1, and while you are putting in the last 6 pieces spam 2, this will assemble the edges of the puzzle and show you the image for reference.
Spamming 2 will keep the unattached pieces on top of the solved part.

It took me around 2-3 minutes to complete 10 puzzles this way.
So put on a good YouTube video in the background and strap in for a 1 hour and 30 minutes of solving the same puzzle over and over.

If this guide helped you with an achievement, I would love a Like on this guide.

If it helped you get 100% a Favorite would help this guide get boosted to others that might need it.