I found iCompta would not accept the OFX file for Apple Card, so I exported a few transactions from the app in OFX format and compared the files. The Apple Card OFX file was missing a few closing tags. I found by adding the lines
</CCSTMTTRNRS>
</CREDITCARDMSGSRSV1>
right before the closing </OFX> tag, I could get iCompta to parse the file correctly and import the transactions.