I was married for 27 years, I have been there did that , soon you will be good at everything, Cleaning, cooking , Building things , Gardening and much more.

Maybe.
What do you mean by "gf?"

Is she actually your "gf?"
Meaning you've dated for a while, learned to communicate, kinda know each other, monogamous towards each other?

Or are you using the term "gf" just as shorthand to denote "one of the chicks I'm sleeping with, possibly the only one because I don't have time to find another. I don't really remember her name, just her screenname since we met online. She's a girl, she's a friend because that's all I'll commit to, we get along as long as we don't talk about anything meaningful or relevant. Really, I don't want to talk at all, I just want to have sex and do things that feel good and I enjoy, and she's sticking around."

If the former, then I don't see how it can't be "okay."
She knows what you're doing.
At best she doesn't care and goes along with it, she might like sex too.
At worst she's taking notice of how to manipulate you, or building up things to use against you in the future. "Well, you did x then, so you should do z now."
People develop relationships that work for them to get them what they want and need. You can either be an active participant in the building/defining, let her do it and force you to abide by her decisions, or go find someone else that wants to build something that considers your tolerance levels.



Or maybe the question is something different.
I mean you labelled the thread "Blackmail."

So I wonder if the question is more like "my girlfriend is demanding I fulfill something, or agree with something, is it okay that I comply even when I don't want to, because I fear she is going to withhold sex if I don't?"

Then it's "okay" as long as you're complicit with what she's doing.
But you going along with it is basically saying her only purpose in your life is to give you sex.
Lots of people are fine with transaction based relationships.
But like every other market/product anymore there is inflation, and she's going to keep demanding more, as well as consistency with what you've been doing in the past, all while trying to give you less of what you want.

Truth!

agar app ko ramu kaka bana hai toh theek hai

Go with the flow..?