Can you efile using turbo tax if you claim form 3800, qbi?

Yes, you can Efile with Form 3800. Click this link for info on Claiming Form 3800 General Business Credit.

If you are referring to a Qualified Business Income Credit Carryover (QBI), this link gives info on QBI Carryovers. 

Turbo tax doesn't let me efile my 2020 return due to a qualified plug-in electric vehicle credit carryforward from last year in form 3800, part III.  I was able to efile 2019 return using form 3800 to claim credit. How  does that happen? Can I find ways to efile 2020 return?

The IRS establishes the parameters that must be met to allow your return to be e-filed. So, it is doubtful you will be able to e-file it if TurboTax says you must mail it in.