For five days a week, I do an upper-lower split. I tend to do lower body Monday, Thursday and Saturday, and upper body Tuesday and Thursday, taking Wednesday and Sunday off (I may do cardio stuff those days).
My priority at the moment is legs, due to a bad knee which I’m focused on keeping stable and strong. You could switch this to having three upper days per week with two lower, if you’re more focused on upper body growth. Or you could even do a push-pull-legs, but then you’d only maybe hit legs once a week, which I think is too little personally - again, all depends on your goals.
With any split, you can easily find a free starter program if you look around. Then you can tweak it based on your own needs. As an example of the content: for my upper days I focus on hitting upper back, lats, some lower back, chest, front, side, rear delts, as well as biceps and triceps. And I add abs at the end. For lower body days I do glutes, quads, hamstrings, calves, adductors and abductors. Sometime o add abs on leg days too.
Which exercises you specifically want to do for each muscle is really down to preference. If you’re very new to it, you could start off with machines, and over time you can tweak your programme to be more varied e.g. with free weight, cables etc. The main thing at first is to learn the form of each exercise, and to track your reps and weights, so you and progressively increase those over time, for growth.
A PPL split is a great choice, so no need to switch to full body unless you want to.
I also find doing full body takes too much time on a given day. My current approach is an upper-lower split instead. That way, on weeks when I can only hit the gym 4 days, all muscles are still getting stimulation twice in that week. When I can more consistently go 6 times per week I tend to do PPL.
The main comment I would have, which has also been mentioned by others, is you probably need to specify your goal (e.g. hypertrophy vs strength?). Then you can research the ideal rep ranges for that goal, as they can differ.
And most importantly, you need to plan for progression - you need some form of creating ‘progressive overload’ in your programme. If your sets and reps are always static at 3X15, then how will you do that? It may not be realistic to increase weight each time, but you could increase reps over time, up to a higher limit, and when you’ve reached that, you then increase the weight and start at a lower rep number - rinse and repeat. There are many other approaches to this too - so find what makes sense for you.