I only found this out this week......
Lateral flow tests are for use without symptoms
PCR tests are for use WITH symptoms.
So many people don't know this! And I think it is why so many think lateral flow tests are rubbish, because they often give false negatives when symptoms are present.
I had symptoms, had negatives for 3 days before I finally got a positive, confirmed by a PCR (Covid has swept through our household this last week)