I had the same doubts. I have also booked Mumbai to Toronto flight via FRA. I contacted the airport to confirm and this was their response -
"
Passengers can transfer as usual in the moment, they only have to wear a face mask and maintain social distancing in the terminal building. They won’t need a negative COVID 19 test to stay at the airport, fill out a form or do quarantine.
Please ask the airline if they would like to see a COVID 19 test before boarding.
"
I dont think the transit would be an issue
"
Passengers can transfer as usual in the moment, they only have to wear a face mask and maintain social distancing in the terminal building. They won’t need a negative COVID 19 test to stay at the airport, fill out a form or do quarantine.
Please ask the airline if they would like to see a COVID 19 test before boarding.
"
I dont think the transit would be an issue