Muscat is strung along about 40 kilometres of coast, and the sights are spread out — Muttrah, Old Muscat, the Grand Mosque, the Royal Opera House, and the beach hotels are each a drive apart. Public transport is minimal; Mwasalat runs some city buses but they are slow and not geared for visitors. The easiest way to move around is by taxi or, increasingly, ride-hail apps (Otaxi, Careem). Metered orange-and-white taxis don't usually run the meter; agree a price before you get in.
Renting a car makes sense if you plan any day trips. Roads are excellent, signage is bilingual, and driving is straightforward. A 4×4 is worth the upgrade if you plan to head off the main roads — to the wadis, to Jebel Akhdar, or into the Wahiba Sands.