What is Error: self-signed certificate in Angular, does it affect anything?

enter image description here

im trying to do a simple cors between Angular and asp.net. Geting data from api works/run fine, but this error keep coming up in Vs code.

I dont understand what does this error affect if everything comunicate fine between Angular and asp.net

I tried following this video to get a self-signed Certificate, but nothing seems to happen, Angular still run, still fetch data, but error is still red.

The video teaches:

1. Create a certificate.cnf in angular
2. Create a ssl key

openssl req -new -x509 -newkey rsa:2048 -sha256 -nodes -keyout localhost.key -days 3560 -out localhost.crt -config certificate.cnf

3. Add certificate in Windows MMC
4. Run Angular with custom certificate

ng serve --ssl --ssl-cert C:\angular-https\localhost.crt --ssl-key C:\angular-https\localhost.key