If you look at the Current Firmware box, you are running firmware version 4.3.25
NOTE: I am not an employee of GL iNet. I am just a user who owns an AR750S and used to be passionate about this router and about GL iNet.
I feel the 4.x firmware for this router is a mess. They removed a lot of features, including file sharing. Before I retired my AR750S, I was still running firmware 3.212 because it was stable. My testing of various 4.x versions did not go well on any GL iNet products I own.
If you look here: https://docs.gl-inet.com/router/en/4/interface_guide/network_storage/#supported-models
They claim they support SAMBA in the beta 4.7.2 firmware for the AR750S. This is beta software that has not been updated in almost a year, and since the AR750S is well past End of Life, I do not think it will ever be released as production firmware. Maybe @alzhao or @bruce from GL iNet will comment once the Chinese New Year shutdown is over. For more information on 4.x firmware for the AR750S, see this post: GL-AR750S-EXT Slate update firmwaare - #30 by alzhao
My recommendation is to load the Legacy 3.216 firmware and follow the documentation you were looking at. You can find it here: https://dl.gl-inet.com/