It seems like there are quite a few people in the same boat (ourselves included). Whether or not a tax return is accepted seems to depend on your local embassy. For example, pre-COVID-19, the US Embassy in London was issuing RFEs to people who submitted tax returns rather than tax transcripts with the I-864. Whether this will now change given the lack of availability of tax transcripts, I'm not sure. Before Covid, people were able to speak to a representative on the IRS helpline and have their transcripts faxed over to an online (virtual) fax number. Hopefully, once some semblance of normality is restored this will be possible again.
