A reader recently asked: “What is the best software and the best OS to operate digi modes with g90”

Well, to each guy his own, but I will say the following: I use almost any software, and often times run it on Windows and sometimes run it on Linux on the raspberry pi. They all work one way or the other, but your personal preferences can slew the final choices.
I don’t have Apple so I can’t comment on that.
If I have to guess at the easiest to implement under Windows I would say use Windows with flrig to connect to the radio. That gives you a panel on the computer where you can establish comms with the radio and see (on the computer) the frequency and so forth.
Remember this is not the audio part of the connection.
After flrig is working, one or two of the more popular programs are fldigi, WSJT-X, JS8Call, or one of the WinLink VARA products. For FT8, I like WSJT-X and for chat messages VARA is interesting. For RTTY and PSK31 I have used the old and free version of HRD (Ham Radio Deluxe).
Now what makes this complicated is that many hams also want to integrate their logbooks with the program and not all programs work the same way with the various logbooks. For DX contacts I prefer logging to QRZ and the syncing with LOTW. You also need to keep a local copy for backup and be able to import-export the relevant ADIF files.
That takes care of the CAT or CI/V interfaces and logbook issues, but remember that you also need to route your audio between the computer and the radio, and for that there exists a number of devices if you like to buy something ready-made, or you can very easily make your own. The internet is your friend.
I hope this helps.
73 Leon Uys ZR6N