Click to Eleven

Developer made an entire guide for all the achievements, which can be found here: https://store.steampowered.com/news/app/1586220/view/4163085194671390827?l=english but ill just quickly summarize it here.

1 to 11 are obtained by left clicking until you hit 11.
-1 to -11 are obtained by hitting backspace until you hit negative 11. -1,000,000 and -999,999 are for exactly what they say.
mute/unmute - mute and unmute the game by pressing M
play - given on launch
rebel - right click.
escape - press ESC.
tab - press TAB.
I'm Broke - when your background color is red, blue, yellow, Hot pink/intense Red, Toothpaste-y, you will see the dev plug his cashapp when you reach the number 5.
scary hour - have the game open or launch the game at 3am.
pink/blue/yellow/red/purple/gren - when you launch the game, the background colour will be random each time. getting one of these colours will give you the achievement for that colour, so you have to keep relaunching the game to get them all.
A/Q/P/M/J/V/I/L/R/U/D/Y/W/K/O/X - press those respective keys.
Rainbow. - When opening the game, you have a 1 in 250 chance to get a rainbow background (and ofcourse the achievement), so you have to keep relaunching the game until you get lucky.