I've done some further reading and came back to say I figured it out, but you guys were quicker -- thanks for the replies. So my understanding was correct: given they have EU pre-settled status, and that being their only residency permit, they will be required to obtain settled status after 5 years ...

Asking for a friend (no, really) and his wife who are both EU nationals pre-settled since early 2019, and also employed in the UK since then. Last month they traveled abroad due to pregnancy. They may have to remain abroad beyond 6 months. They continue to work for the same UK employers remotely fro...