Does Arrotel Transit Hotel Singapore need to enter the country?

Of course you don’t need it if you don’t leave the airport.

If you want to leave the airport, but you already have a valid visa for the target country and a ticket for the next leg. You can enjoy a free 2-3 days tour of Singapore. The Singapore Tourism Board calls this event the singapore stopover. You can directly ask the immigration officer at the immigration gate at the airport, and they will review it directly for you on the spot.