Screenshots and/or screen recordings help a lot in debugging a technical issue. Please see below instructions for different systems.
Windows
Use the built-in snipping tool: In Windows 10 and later this works with all browsers. You can use the PrtScn button or the combination Windows + Shift + S.
To take a screen recording (available if your system is updated) you can click on the camera icon, or use the combination Windows + Shift + R.
Use the Xbox Game Bar for screen recordings: This works on Windows 10 and later with all browsers; it only captures 1 screen at a time (the active screen). To activate it, press Alt + Windows + R. You will find the recordings in the folder Videos > Captures.
Download & use Flameshot
Download & use ShareX from their website, or get it in the Microsoft app store
macOS
Use the Screenshot toolbar: To view the Screenshot toolbar, press these three keys together: Shift + Command + 5. You will see on-screen controls for recording the entire screen, recording a selected portion of the screen, or capturing a still image of your screen.
Use QuickTime Player: Open QuickTime Player from your Applications folder, then choose File > New Screen Recording from the menu bar.
Download & use Flameshot
Linux
Use GNOME's screen recording tool: If your distribution uses a recent version of GNOME (like Ubuntu) or derivatives (like Cinnamon on Linux Mint), you can use this tool. You will find the recordings in the folder Videos > Screencasts.
Use KDE’s screen recording tool Spectacle
Download & use Flameshot
Find some other alternatives
What about mobile devices?
Screenshots and screen recordings from mobile devices are not very useful to us. They don't display all necessary information because of the screen size. Please use a laptop or computer.