I am a dual UK / Irish citizen currently living in the UK. I like to carry my Irish passport card as it is small and convenient. I could hop on a plane, train, or boat to the EU (and some more countries) without going home to get my passport book. However, this is in doubt now as I have heard that EU ID cards can no longer be used to enter the UK. The Irish DFA site suggests that it is still valid. However, this is not a UK government site and hence it might be out of date or incorrect. At the least, it is probably unconvincing to a UK border official.
If I cannot reenter the UK then the value of the card to me will be diminished significantly.
Note that I am not only asking about entering the UK from Ireland but also from other countries where my passport card is accepted.
I have now figured it out but I thought that it might be useful to others so I plan to self answer.