If you travel on 1 ticket and with a transit in FRA, you will not enter Germany and do not need to fullfil German Covid requirements. You will be asked to show Covid documentation at check-in.
Most likely the check-in agent will not be interested in your onward journey. Just have your DEL-BKK ticket/e-ticket receipt ready to show at check-in or immigration in India, if needed.
2 hours at FRA is more than sufficient; when you are traveling on 1 ticket there is nothing to worry about. 99% chance that you will make that connection.