Might want to sticky this.
https://drive.google.com/drive/folders/1e_hQNQiJVxhHP_5WBQhBNur9dnS5ml3E?usp=sharing
Never run out of puzzles. There are well over one million puzzles.
The Zip file is all the other .sdm files together, and its barely larger than the largest single .sdm file. It's less than 37 megs.
All converted to the .sdm format, which you can install into some apps. Notably Sudoku 10,000. Not sure which other apps.
NOTE: To install into Sudoku 10'000, you need a real File Explorer. AMAZE is the one most people use. It's free and does a wonderful job. Just launch AMAZE, find the .sdm file on your phone, and "OPEN WITH" Sudoku 10'000.
You can change the format to one other fairly easy, by just find/replace all the zeros to a period.
You can download the Easy, medium, hard diabolical as a text file from Sudoku Exchange website. It's not in .sdm format though. But it does rate every puzzle in the text files.
Pearly6000 are extreme puzzles.
Superior160 are weekly hard puzzles from Times (London Newspaper), or similar publications.
17puz49157 is unsorted, but is nearly all the 17 clue puzzles identified so far. 17 clues is the minimum number of clues needed for a proper sudoku puzzle. So it's a rather special collection.
Almost Daily Nightmare are less than Nightmare level from Sudocue.net
Learning Curve are puzzles that gradually get tougher. A day one beginner should be able to do the first puzzle.
Easy and Medium both are 2.4 SE or less. I assume the medium puzzles are a bit more tricky.
Hard puzzles are from 2.5 SE to 4.4 SE.
Diabolical are harder than 4.4 SE
No One Trick Ponies. Not sure the difficulty, but most likely at least 4.5 to 6.x SE
TOP_50K_Toughest are tough. Most likely topping out at 11.9 SE. It's designed to test sudoku solvers for budding programmers. But they can be solved by talented humans.
Happy Solving.
