If you decide to not own a bike in Germany, there are several options to go to work or visit Frankfurt by bicycle:
Call a Bike
I recommend Call a Bike where the daily rate is 9 euros. If you live in Frankfurt you can pay 49 euros per year to have unlimited use (periods of 30 minutes).
If you need a permanent bike, and you can’t deliver the bike in stations, I would recommend Swapfiets. It costs €16.50 per month and you get one bike for you. There are other options more premium that include an e-bike.
nextbike is a service similar to Call a Bike. Also costs 9 euros per day if you are visiting Frankfurt, but the price is more expensive if you plan to use every time: it costs 10 euros per month.
Bicycles are perfect to visit a city. You can basically park almost everywhere with the daily plans. Is a transportation without pollution and people end up doing exercise.
Bike Citizens app has some curated tours by bicycle that you can do while visiting Frankfurt.