Do I need an appointment to buy a computer

Naaa just go innn ...

Yes you need an appointment for anything if you don't have an appointment they may still see you but you're going to be waiting for at least an hour or two no exaggeration was just there waited 30 mins with appt.

I was in si mall 2 weeks ago and the apple store was packed inside and outside the store

You can't buy from inside the store anymore you have to order Online and then pick a specific location if you choose too and then go pick it up make sure you have the pick up information email it will have the QR Code in it and ID.

With Covid it's best to make an appointment since Apple is always crowded, the line to just go in without and appointment are long and they don't social distance on the line so you're really close to other people. An appointment is best unless you want to wait 2 hours to get in.