Does urgency always indicate a flare?

Normally holding in bowel movements decreases urgency and can even induce constipation. You can definitely have urgency despite having solid stool and it may or may not be indicative of a flare. Let your doctor know so right away so they can run bloodwork and a probably a fecal calpro.

Inflammation is certainly one source of urgency. But motility issues (including spasm) can also produce urgency. I suspect that while holding bowel movements can induce constipation for some, it can also have other consequences. The body and its feedback systems are not designed to have stool held in the sigmoid or rectum for several days. Once you are doing this all bets are off.

I would work to eliminate on a more regular schedule, and just monitor the urgency issue. If you don't see blood, the urgency may be less likely to indicate a flare.

good luck