Is there anyway to allow Single Choice & Multiple Choice options to be selected with tab key?

Please note that tab works fine with the single & multiple choice question. It seems the theme you are using is causing this issue. If we change the theme of your form, the tab feature works just fine.

Can you please let us know which theme you are using? I did check your form and found that you are using default theme but your form has several custom css code injected. Have you manually injected the custom css code in form or it was added automatically when you applied a theme?

Do get back to us on this and we will escalate it to our backend team.

We will wait for your response.

I think it was a hotel reservation template.  I did not add the custom css code.

Is it easy to change the theme of the form?

You may change the theme and see how it works for you. It's very easy to change it as well. Here is the article that helps you - How-to-Apply-a-Theme-to-Your-Form 

Let us know if you still encounter any issues. I hope this helps.