Is tere no ig Bus (or Tootbus) that goes to Montmartre during the day?

The Tootbus goes to Montfart, not Montmarte.

As the name suggests, Montmartre is built on a hill. (Mont=mountain) This means that streets of Montmartre are steep and narrow. The streets aren’t even that suitable for cars let alone for those big tour busses operated by Big Bus and Tootbus.
The best way to explore Montmartre is on foot. If you have trouble walking, you can perhaps take a taxi to the top of the hill and explore on foot from there.

Yes, the streets around Montmartre are too narrow for tour buses. The best way in is to get the Metro to Abbesses station then walk or take bus 40.

There's a RATP (public transportation) bus that goes to the top of Montmartre, as does the little tourist train.

You can take the metro to Lamarck Caulaincourt or Abbesses both of which have elevators to the surface. There is a small bus that goes to the top of Montmartre. There is a little mini tourist train and although I would feel like an idiot on it, if I had never strolled through Montmartre and were now too old or infirm to do a lot of hill climbing then that would be a great way to see some of the pretty streets. I believe you can get off at Sacre Coeur and catch a latter mini train back down.

Big Bus type tours go where it is easy to drive not where it is most interesting to see and in Paris as in many other places, more interesting parts of town are not easily reached by double decker waity waity waity buses.