Going to be in Frankfurt 2 or 3 days.

Take a Frankfurt on Foot walking tour.

seconding TexasTravelmom's suggestion. You won't regret it

thirding TexasTravelmom's suggestion.

Top things to see?

Kaiserdom
Karmeliter Cloister
Jewish Holocaust Remembrance Wall
Frankfurt Höchst Alt Stadt - Markt on Tue. Fri. and Sat. 7-13:00
Kleinmarkt Halle
St. Leonhards
Alte Nikolai
New Alt Stadt
Alte Oper
Palmengarten
Deutsche Orden Kirche
St. Justinus Church
Konstablerwache Market - Thur. and Sat.
Schillerstrasse Market - Fri.
Bethmann Park with the Chinese Garden
Main Tower

Restaurants - Dauth Schneider, Lorsbacher Thal, Apfelwein Dax, Zum Schwan, Zum Bären, Alte Zollwache

Thank you for all the recommendations. This will help a lot. Will let you know how it goes.

I’ll be the 4th to recommend a Frankfurt on Foot walking tour.

visit NFT bar and enjoy the whole view of Frankfurt , I was there 2 weeks ago there was a waiting line of 30 minutes to enter the bar, the view is incredible of the whole city service was slow but who I am to judge the view was enough for me.

And I’ll be the 5th to recommend a Frankfurt on Foot tour. Take the first available tour so you can see the many things Frankfurt has to offer and plan your remaining time more efficiently.

https://frankfurtonfoot.com/

So as not to be a 6th, I'll second Mona's suggestion to take the Frankfurt on Foot Walking Tour early in your stay. It gives you such a good overview and see so many sights to help you focus your own time afterwards.