Mirroring doesn't work

Get help with video issues on external displays connected to your Mac - Apple Support
 https://support.apple.com/en-us/HT201177

You can Try using Extended Desktop Mode instead of Mirror Display Mode. Mirror display also mirrors the display resolution. Extended desktop mode allows you to select the native resolution of the external display.

See if you still have this option >System Preferences>Displays

press the Option key while you're in Displays— You'll get a Detect displays button (bottom right).

there is a checkbox "Show displays in menu bar". If you check it, you get a new icon in the menu bar that has "Detect Displays" as its first option.

Use external monitors with your Mac: https://support.apple.com/en-us/HT202351

I liar144 Said:

”Mirroring doesn't work: [...]when I look for the ‘arrangemnet’ tab in the ‘diplays’ under “system preferences’, it disapeared as well- the tab is not there. What can I do?”

———-

First Reset your SMC and your NVRAM:

Sometimes changes are made to the system and then settings (i.e. for the displays) become manipulated, technically. So, reset both on your Mac. 

If that does not work...

Shut Down the Mac - Unplug the Display:

If the screen is still not showing:

1. Shut Down: your Mac
2. Unplug: the screen
3. Wait: 30 seconds
4. Plug: the screen back in
5. Power Up: the Mac

See if this now all works!