I M not facing any such lag....however if u r facing this it ll be fixed through an update....don't worry stay happy.

U can expect a beta release of Android 12 for ur device after it gets released for S21 series which is just round the corner......by the time u might get stable version of Android 12 on ur device though.

U can directly order screen protector from spigen India website or Amazon.in....they are thin n good...still if u want a tempered glass gi for whitestone dome glass...little expensive but bestu can order through Amazon.