I’ve currently gained a bit of weight (6’ 245 lbs) and have gotten somewhat weak. If I practice shooting prone unsupported will my current physicality  affect my shooting and prevent me from getting better or is all just a matter of technique and I should practice regardless of physicality? Or should I wait until I have my health back before practicing shooting prone unsupported. Or does my physicality not matter much and it’s more a matter of technique.

Oh this also applies to shooting kneeling as well. If I lose the weight will I notice a big difference or is it more a matter of technique

Join the militia?

Ok serious answer being fat makes everything harder except sumo wrestling. Lose weight, gain muscle and shoot all at the same time.

You mean I should practice shooting prone even if fat

prone will be fine

So i'm good to practice and don't need to lose weight first?

OP,
There’s no reason for you not to shoot. Go for it and have fun. Even in poor physical condition you’ll be able to do well with practice.

To do your very best I would encourage you to work on improving your physical condition though. You mentioned shooting prone unsupported which gives me the impression you are thinking about competing in High Power, Palma, or a similar discipline.

You can train and compete, and with practice will do well, but working on your physical condition will also help a lot. Shooting a 20 shot unsupported prone course of fire can be physically exhausting. It will be less exhausting if you get in better shape. Also, improving your cardio condition will improve your prone scores. Poor cardio = rapid heartbeat = can’t time shots between beats. Even with the best technique a pulse beat moves your point of aim. If you improve your cardio you can make pulse less of an issue.

Start by doing some unsupported prone dryfire at home. Time it like a match and this will help you get an idea of your physical limitations. If it’s too hard to do a full session the first try, just keep training to work up to it.

Qualifier: I shoot on a state rifle team, coach high power, and have won some stuff. ; )

Go prone, shoot 1 round, stand up, shoot 1 round. Repeat until mag is empty. Then do that for all your mags.

Use a sling. It’s fine to start working.

Just do it, man. If you decide to lose weight, you'll probably have to make some adjustments; but can you guarantee that you'll lose it? I'm not trying to be a dick, but many of us--including yours truly--set a lot of great goals for fitness, and never follow through. If you keep waiting for something like that, you might never achieve either.

You may get a kink in your neck from having to crane it higher, but other than that . . . YES!!!! You're gonna suck!!!

Hahahahaaaaa!!!!!

ETA: Just messin' with ya, OP! Go have fun!!!!

What kind of shooting are you wanting to train for? Defensive situations? Competition? Just blasting?

If blasting, just do it, it doesn't matter anyway.
Competition, if you plan on competing while at your current wait, practice.  If you want to wait, work on things like trigger control and reloading. You can do this seated at a table, just to get a feel for it.
If for defensive situations, are you going to ask the potential assailant/attacker to hold on and come back in a few months when you've lost weight and are healthier? Practice now so if you need to use it, you can use it.

Of course being overweight and out of shape will make things more difficult.  Practicing will help some, but getting into some semblance of good shape along with practice will make a giant difference.

Being in shape will make it easier to get into positions, which will in turn keep your heart rate lower, will in turn make you shoot better.  

Getting stronger will have obvious benefits.  When I was doing lots of shooting, I had an old rifle stock with a 3' long piece of 1.5" diameter solid steel rod strapped to the stock with radiator straps like a giant rifle barrel.  I used to see how long I could hold it in the offhand position.   After a month or so of daily work with my device, offhand shooting got MUCH easier.

Getting into prone is a lot easier than standing back up. AMHIK.

Should you practice? Yes. Should you wait until you are in shape? Not unless practicing in your current condition is unsafe for your health.

Will you get better? Absolutely. Will you reach your peak ability without getting in shape? No.

My prone score averages in high-power improved notably year-over-year when I went on a training program that increased strength, endurance, and lowered resting heart rate.

So, in true arfcom fashion, get both. Start shooting now and start getting back in shape now too.

OP, you will never be at the top of your game if you are not strong and physically fit.  Good physical fitness is a crucial part of training.

Sure, get both, you can work on various aspects of practical shooting, associated TTPs, and drills starting now, but you should be working harder on getting in shape, based on what you describe of your own condition.

It is in some ways the hardest part of true readiness, and is often overlooked.