No, it doesn’t contradict. What I said that for any given moment, for any infinitesimal duration, the “relative” acceleration would be 9.81 m/s2.
Oh, so you just disagree with the definition of proper acceleration. Amazing. Perhaps stop using that term and define your own, then?
Proper acceleration by definition cannot be relative.
This continues to be factually incorrect, and you were provided with an explanation as to why. You're gonna have to address it, instead of simply restating the same error over and over.
For the sake of argument, imagine someone else in an inertial frame in a galaxy far far away perceives earth’s “relative” acceleration as 7.2 m/s2. Does that mean “gravity” is weaker on earth? What if someone else in another inertial frame perceives it at 12 m/s2? Is" gravity" stronger?
Keeping in mind what time dilation is (and that you failed to account for it) - yes, that is more or less correct. If you somehow managed to observe the Earth from one of the FoR's you described, your observation would be drastically different from that of a local observer on the Earth.
If you are accelerating in a car at 100mph, you will experience physical effects from that. You will feel it.
Applying classical mechanics to a discussion on special relativity is a schoolboy error. Don't waste our time with that.
You can’t have it both ways. Either the earth is constantly, physically accelerating at 9.81 m/s2 or not.
Welcome to the amazing world of relativity, where the things you consider obvious and intuitive are completely wrong. Enjoy your stay, and do some reading before you humiliate yourself again.
If there is an infinite number of inertial frames and the earth’s proper acceleration can be perceived at an infinite number of different rates…how can FET say it is accelerating at any specific one if it can't be objectively determined? For that matter, how can FET even say that it is accelerating at all, if you can’t determine it objectively? Has any flat earther ever observed the earth from an external inertial frame?
The very core of relativity is that there is no objective frame of reference. It's not that FET can't determine these things objectively - it's that your idea of being "objective" doesn't exist in physics. The core point here is that a frame of reference in which the Earth exceeds the speed of light cannot be defined. We focus on two reasonably observable FoR's - a local observer, and an arbitrary external inertial observer. Those are the "important" ones to explain, and we've covered them both.
We can say that the Earth is accelerating relative to a local observer in free-fall (as we do), because we're local observers, and we can easily verify this. This remains true in FET and RET alike. You can jump off a chair (please do so more competently than most other things you do - be careful not to hurt yourself), and, taking your body as the frame of reference, you will observe the Earth accelerating towards you to meet you.