Hardgainer over 40 looking for advice to finally put on some muscle

Another way would be to run a simple Push/Pull/Leg routine, or a 4 day body part split divided over 8 days.

That way you could run and Evaluate a plan that gave each part more work and more rest, to see if it works better for you than full body.

And you’d get a feel for how an experienced author/coach fits all the body parts into a training week, and how much work they think is necessary for each “part.”

If it sucks, doesn’t work and you hate it, you can go back to full body in 8 weeks. And then you wont have to worry and stress about “what if,” you’ll just know.