PySimpleGUI, according to its documentation, is a wrapper around four frameworks: Tkinter, PyQT, wxPython and Remi (something webby, again from the docs).
So, in order to make your software accessible, you need to know what is your underlying framework. Tkinter (which, I presume, is the default) cannot produce accessible environments at all as of October 2021. PyQT requires some work to be able to do it, but I don't know whether PySimpleGUI provides those tools. The same is for Remi: webby environments can be accessible, but I have no idea about what PySimpleGUI provides accessibility-wise.
wxPython is the best choice here, it is known to power lots of accessible apps (including NVDA itself, ironically!). So I would go for wxPython as the underlying framework.