Display

1060b wrote:

I tried to enlarge the font size and now the colors are really vivid and distorted

Vivid and distorted it sounds like you made some change in the Accessibility

>System Settings>Accessibility

A SafeBoot Use safe mode on your Mac - Apple Support will sort many anomalies

Login and test make some changes. Reboot as normal and test.

>System Settings>Display> Default display resolution is universal...

Keyboard short cuts are app specific...

Command + increase

Command - decrease

Command 0 default

(note: no shift key involved here)

ref: Mac keyboard shortcuts