HMRC has published details of what returns must be submitted on paper as software cannot cope.Self Assessment technical specifications (2022) for individual returns - GOV.UK
"1. Most developers will have taken the following items into account in their software. If a customer does find though that they cannot file online for one of these reasons, a claim for reasonable excuse should accompany the paper return.
And "Where a personal return cannot be filed online for a reason listed below, provided that a paper return is delivered on or before 31 January following the end of the tax year to which the return relates, HMRC will accept that the taxpayer had a reasonable excuse for failing to file a paper return by the normal 31 October deadline. A reasonable excuse claim should accompany the paper return. "
Any paper return submitted must conform to the normal rules for paper returns even if it is a computer—generated paper return e.g., it must hold a valid signature.
Where an HMRC recommended workaround causes an online return to be submitted with an entry that is not strictly correct, HMRC will not take action on that particular entry for that reason alone provided that the inaccuracy is in accordance with the workaround and purely to facilitate online filing."
HMRC are giving away free reasonable excuse claims with certain select returns. Bring on MTD ITSA!