You are up against two IRS restrictions. These restrictions are imposed by the IRS, not by TurboTax.
1. An amended return for a change of filing status cannot be e-filed under any circumstances. It has to be filed by mail. An e-filed amended return must have the same filing status as the original return.
2. You cannot amend from a joint return to separate returns after the original due date of the return, even if you file the amended return by mail. (Separate returns means any filing status other than married filing jointly. It does not only mean married filing separately.) As macuser_22 said, there is an exception if the joint return was not valid because you were not legally married as of December 31, 2019, but the amended return still cannot be e-filed. The procedure for amending an invalid joint return is very complicated, involves a lot of paperwork, and essentially requires professional help.
@charlesusa wrote:
I already sent a paper return before the due date 16 weeks ago without any confirmation.
Any paper return that you mailed 16 weeks ago was delivered during the time that the IRS processing centers were closed because of the Covid-19 pandemic. It is sitting in one of the large trailers full of unopened mail that are parked outside the processing centers. The processing centers just recently started to reopen and begin processing mailed returns, but they have reduced staff and a huge backlog, so it will be a long time before your mailed return is processed or any status information is available.
If you already mailed a return, do not file another return. The IRS web site says the following.
"We're experiencing delays in processing paper tax returns due to limited staffing. If you already filed a paper return, we will process it in the order we received it.
"Do not file a second tax return or contact the IRS about the status of your return."
