Add cellular plan option missing on iPhone

I have an iphone 14 pro, want to go abroad, found an esim provider with a great price, but im my settings I have no option to add a data plan. I looked at all the similar threads, and all of Apples documentation, and couldn't see anything

I tried resetting my network settings, I took the physical sim out, and in again, and nothing worked.

I asked to use a QR code, it says "cellular plan" but when I click on it, nothing happens. the application of the esim provider tells me that my phone is not supported, but it's an iphone 14 pro, so it must be supported.

Also when I go to the settings I see that there are no sim restrictions. What should I do? what am I missing? this is very frustrating!

[Re-Titled by Moderator]