Just to add to this since I recently went through it. You can just go to the custom records section and hit manage custom records. At the bottom click add and recreate the MX record SPF record and DKIM record and hit save. Google will prompt to confirm overwriting of the synthetic records, just hit yes.
The google workspace record section will be gone. But that was what would happen if you deleted it and then added them back in the custom name records anyways.
Everything keeps working and then you can move forward to adding your custom compound SPF records. It looks and feels way more daunting than it needs to be.