[RichDad]

My legit SG calls also got +65

That's outsourced support calling from overseas but somehow using a Singapore number.

If it is legit for you, then better answer.

For me, no such need at all.

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Government removes “+” prefix so Singaporeans can differentiate overseas calls from local ones
From 15 Apr, all international calls will start with a “+” prefix. On the other hand, all local calls will no longer start with Singapore’s international dialing code, “+65”.

https://mustsharenews.com/prevent-scam-calls/