"apt-mark showmanual" will show you all packages that you have manually installed
"apt-mark showauto" will show you all packages that are automatically installed
"apt-mark showinstall" will show you all the packages that are installed
How is this useful? It tells you what packages are installed in your system.
So you can go "apt-mark showinstall | grep somelibrary" to see if you have a particular library installed that's a dependency.
Gyruss Game Cartridge for Atari 8-bit Computers 400/800/800XL 1984 Parker Bros.
$39.99
Defender Game Cartridge for Atari 8-bit Computers 400/800/800XL/XE 1982 CXL4025
$29.99
Atari 600 XL Vintage Home Computer - IN BOX W/ Manuals, Cables. Clean Console
$175.00
SALT II Atari 400 / 800 System Stand Alone Test Revision 2.04 VERY RARE
$59.95
Pitfall Game Cartridge for Atari 8-bit Computers 400/800/800XL 1984 Activision
$119.99
Vintage Atari 800 Home Computer Untested
$139.99
Vintage Atari 800XL Computer *UNTESTED* No Power Cords Or Cables
$99.99
Atari Power Cube 800XL, 600XL, 65XE, 130XE USB-C Power Supply PSU
$11.25
A8picoCart Atari 130 / 65 XE 800 / 1200 XL XEGS multicart UnoCart clone game
$32.95
Vintage Atari 800XL Computer Powers On Untested - NO CABLES OR ACCESSORIES
$124.87