Let's look at this for a change.

Do you think having a close friend of the opposite sex is a red flag? Or is it ok?

I have seen girls having a guy friend whom they talk anything to like their problems with their bfs, their personal well being, their personal history bla bla bla.

I have also seen guys doing the same thing with girls.

What are your thoughts on this?

There was once I always make fun of them saying they are a thing but they seemed to shy away whenever I did that and just remained silent.

not possible. sure will kena makan sooner or later.
man and woman cannot be best friends one.

why not should be fine , close friend doesn't mean must be same gender

It shouldnt be a problem. I have a number of close female friends, including my ex-Sugar Baby 😆

Its how you treat your SO relative to these friends that matters.

ok a... just do not think of eating them

true , it's all in your mind , if you think that person is your good friend , treat them nicely , not more then that

Generally speaking, having more female friends will open yourself more opportunities to meet other people. Just dont invest yourself blindly onto a female who doesnt reciprocate your interest

I answered this in the past:
In your context of trying to find a partner, I would not consider anything as red flag yet.

I have multiple close female friends that I can travel alone with or in a group and stay in the same hotel room although separate beds.
I just dont see them that way and they dont see me that way.

Not feasible. Its like wheeling a starving man thru a buffet line and not allowing him to eat anything.

If the man is well fed with delicious food, the buffet wont look appetising.

you guys might think it is ok, but the woman might think differently
after few drinks, some things might happen
dont want to regret later.

I'd rather think it's more towards the relationship status of one side vs the other, not so much the gender.

If both are single, then there's nothing to go "wrong" because no one's cheating on anyone. Congratulations!
If one is single and the other isn't, there is a higher chance that something would go wrong because one side is still searching and is more likely to "cross the other's line".
If both are not single, then I believe it is harder for something to go wrong, but when it does, it's a 4-side explosion.
In all cases, there's no point to discuss if the person in question oversteps his/her boundaries so I'm speaking for generally responsible adults. In a committed relationship, both have the responsibility to ensure nothing goes wrong... E.g.
- if your other half is insecure then avoid 1:1 with opposite gender or "report in" more often.
- if can't hold your drink then don't drink lah

If your partner's insecurity feels suffocating to you, that means there's misalignment on expectations and you need to talk it out, or else it's the end lah. This is one of the "values" to evaluate during dating stage, because some people's expectations may not be something you want to comply with (read: don't stick your d in crazies).

Hahahahahaha! Base on life experience, 101% Impossible!

You might think it is ok, but your partner will never think it's ok.

I think what TS is trying to ask is whether a purely platonic relationship can exist between 2 heterosexual members the opposite sex.

In a professional sense, of course - some of my colleagues and I have passionate arguments over the best course of treatment for a particular patient and my wife knows better than to get between 2 dogs fighting over a bone (she is - was (retired last year) - a chartered accountant).

In a social setting, only if the lady is married - then, the boundaries are clearly defined and drawn. The group of Uni classmates from medical school I still hang out with have their wives (a few are fellow doctors, most are not) join us, and as usual, like personalities will gravitate towards each other, but we also know that when it's time to go home, we go home with the correct partner.

In any other setting, especially if alcohol is involved, a flat outright NO.

Well yes, I don't agree that a pure platonic relationship can exist between 2 heterosexual parties. Once I seen 2 couples. The guy is very close with the other girl. End up, they slept and there we go.

Very difficult to shake of 300,000 years of biological hardwiring.

Platonic relationship can only happen if there's no sexual attraction/chemistry between them.

If one of them is attracted to the other, then got problem. Don't care married or not.

There can be love between the 2… platonic love, meaning, they care deeply for each other, but just not in a sexual way.