As is typical of the time, there is nothing in this bathroom that meets today's building/plumbing codes and there is not enough space to utilize universal design or aging in place concepts.

Can you open the wall to the shower to go all the way across the room so that you have at least a little space to scoot by the toilet?

If you start trying to move the toilet, then you must comply with current building/plumbing codes and you cannot in that room. Then you can get yourself into a real mess. Long term what we see many people doing is taking an adjoining room and opening it up to the master and using it as a new master bath. The old bath is generally reworked and combined into a closet space as additional closet.

The only possible way I see to provide an accessible shower in the existing space would be to make the whole space a wet room. Even that would be a very tight fit and has its own problems. I'm afraid you're going to have to bite the bullet and find space somewhere.

I'd create a floor plan including ALL the surrounding rooms, closets, etc. and start thinking outside the box about where space could be found, and how to configure it. E.g. what about making this little room be shower only, or shower and vanity, and then finding a separate space nearby for a little toilet room with handwashing basin only? Or a tiny bumpout of the wall of your house? If you can cantilever it, you would not need the expense of a foundation. (Obviously this would require design by a structural engineer.)

It's good you're thinking about this now, rather than waiting until you have a crisis on your hands. Good luck!