Is it weird to hide a long term partner from friends?

It depends upon the specific individuals motivations, personality and attitudes towards their privacy & sharing details of their private life with others.
There is a lot of difference between been very protective of privacy and being discrete about relationships/dating/hookups and actively hiding a long term partner.

But even if you’re being protective of your privacy, would you say it’s normal for even close friends to not know about a partner?

But even if you’re being protective of your privacy, would you say it’s normal for even close friends to not know about a partner?

It depends on the person's personality and specific circumstances.

My best friend lives in India, we've been besties since we met at nursery over two decades ago.
She tells me about every bf, guy she's considering dating and every date she goes on.
She knows most of my exes where the relationship went beyond 20 days and the majority of guys that I've gone on dates with.
But I wouldn't tell her if I was dating or very closely involved with a guy that was incapable of being civil towards her because of her career, nationality, religious affiliation or wealth level.

And you would date such a guy?

Yes.
I have done.
Plenty of people are incapable of demonstrating civil conduct towards people who are high earners or have inherited assets of a significant value.

So you’d value a guy you’re attracted to over the circumstances of your best friend and how the guy would treat them?

My best friend & I have very different dating dealbreakers and know not to get too involved in each other's & other people's private lives.
Particularly now that many close friends are living quite far away or in different continents.

My best friend does not have the entitled mindset that demands the respect of random strangers.
Nor do I.
Neither of us expect everyone in the world to automatically hold positive opinions of us or our livestyle preferences.
Appearances, backgrounds, choices, personalities or anything else.

The reality is that most if not all adults have at least a few people that actively dislike them and are keen to make the fact obvious.
Best not to needlessly dwell on or highlight the unpleasant comments and antagonistic actions of those who want to cause trouble.
Much better to avoid direct participation in all this type of drama and negativity, including by repeating the gossip or unpleasant remarks.

So would you value a guy you’re attracted to over your best friend? Would you ditch your best friend if your partner asked you to?

It's not a question of comparing the value of one to the other within the contexts of a best friend, date and regular sexual partner.
No, I don't respond well to those who try to interfere in other people's friendships or issue ultimatums.
The last ex despised my best friend and I disliked quite a few of his cabal.
But neither of us made it a big issue during the relationship, even when we were living together.

So would you spend as much time with your best friend if you get a boyfriend? And your interaction with the best friend wouldn’t change?

Yes.
My best friend & I live in different countries, she's in India and I'm in England.
Every day we text, talk over the phone and email each other.

Do you think it would be different if your best friend lived near you and was a guy?

Is it weird for someone to not tell their friends about their partner if they’ve been together for a year?