Why my Oppo is can't switch on if off and can't switch off when it on

@indrabasuki here is a possibility that this is caused by a failed power flex cable. Replace that and then re-evaluate.

Grammar apart, it is amazing how you can structure your issue using no more than 7 characters for each word (I thought `is` is a typo, but typo to what, actually?). The length however also reflects the depth. No model?

Most likely, it is like what oldturkey03 said. Provide more emphasis, like can it be used in other functions, like

- locking and unlocking the phone screen

- taking screenshot (with one of the volume button),

- mute notification (with another volume button),

- activate google assistant/google pay/accessibility features,

- turn off torch in some cases or scanning fingerprint

Oppo phones' power button should at least do one of these apart from switching it on or off. Otherwise, bad questions rarely summon good answeres.