Fast answer
For most first nights in Monopoli, keep dinner inside the old town and use the old port as the low-effort orientation walk. Add a Porto Vecchio aperitivo only if arrival timing leaves enough margin, use Piazza Garibaldi as the central fallback, and leave Capitolo dinner for beach-led stays that have already confirmed transport, seasonality, and table availability.
If you only do one thing
Default to a reserved old-town dinner after check-in, with a short old-port walk before or after the meal. A beach-club dinner is better kept for stays already based in Capitolo, or for groups that have confirmed dinner service, access rules, event conflicts, and the return plan to town.