if I add Custom CSS or change some color using Theme Customizer option ‘additional css’ which comes after homepage settings in theme customization menu in gp. Will it create any problem or will break my site when I next time update my gp theme
No, It shouldn’t break your website (99% certainty). Depending on what your css is and what updates take place then there’s no 100% certainty. Some time ago Tom made some big updates that made my css change the look of website in ways I didn’t want but it was easily fixed by coming on here and getting some great support. as said above, the css in the customiser stays the same after each update (but it’s always a good idea to back up your site before any updates).