Red brake light with exclamation mark comes on

That is the brake pad wear warning light. You either need new brake pads installed or the wiring to the pad sensors has a fault.

Depends on the year, build date and even option packages. Some are red, some are yellow, some show up as text in the DIC.

The center warning is used for a lot of brake issues. Low fluid, brake wear, parking brake, ABS, blown brake light bulb all trigger the same red brake light. There will be smaller lights on the dash or in the DIC to point you at which item it is, but some of those indicate two items.

Check the brake fluid level first, the sensors are "picky".
Next be sure the E-Brake is fully off.
Check the rear brake lights as well, a blown bulb can make the brake warning appear.
If those are okay then it is time to did deeper.

For that you may need a scan tool to see if the ABS is reporting an error or if it is the pad wear sensors. Audi makes things interesting at times. Typical over engineering.