We went in November 2023 to visit a relative, working there. We didn’t have to book accommodation. However, we arranged car hire ourselves - drove to various places in Muscat and into the mountains for a few days stay in a hotel to look at the scenery, forts, etc. IIRC, petrol is cheap by our standards!
I think it might be cooler in December, as our relative told us it was too cold to sunbathe, as it’s only 27 degrees C….
We found a dolphin watching trip in Muscat, which picked the customers up from the big hotels - we walked to one nearby. We have never seen so many dolphins!
I suggest taking long trousers, a t shirt, cardigan and a head scarf, if you want to visit the Grand Mosque. It is stunning! An official lady helped foreign visitors put the head scarf on properly. I don’t think tourists can visit any other mosque there?
We didn’t find it difficult. Avoid PDA, swearing and getting drunk there. We found the people to be helpful, polite and friendly. Language was not an insurmountable problem - even in the mountains, people spoke a bit of English.