RM187 is the retail price for MYTV Advance box.
Watch YouTube? MYTV want you to buy their TV box is only to receive/watch its digital TV channels and its other interactive services, not for other thing else.
No, you can't watch YouTube on that.
Perhaps you can look for Android boxes that comes with DVB-T2 built in tuner at online shopping sites like Lazada and Shopee.

How old is the antenna? If many years already just get a new one to replace. Imo no harm but just to make sure you don't need to go get another antenna while in the middle of setting up the new TV.
Regarding the cable, if my old antenna cable is not the screw type, just need to buy the converter right? or rewire is better? Because older TV usually you just insert the cable into the port, no need to screw. I am very sure this is UHF antenna, just the cable not using screw like astro.
Botato decoder got WiFi or Ethernet port? Can watch Youtube and install app also?