Your guide hand looks like a way bigger problem than your shooting hand.

1) Bring the elbow of your guiding hand in so it's straight and better aligned, the elbow flares out
2) Your shooting hand goes forward a little too much instead of up
3) work on your knees, when you do the above two you will have a straighter shot but you need to exert more power, you will only get that from your knees.

If you don’t have the power from your knees or muscle in the shooting arm, your body will counteract by flaring that guiding elbow out and moving your shooting arm forward instead of straight up.

I had the same issue after being out of basketball during those uni days, you might be strong generally but you lose the critical muscles and knee strength. You regain it by getting work back into them, that starts with shooting without a guiding hand and focusing on shooting close to the basket before stepping back gradually. Takes a month or two before you can shoot reasonably from free throw line and three point line again.

When you need to catch and shoot quickly to avoid defender, that ball stops going in if you have a wayward shot.

Props to the OP for throwing it into Hoops Forum and videoing it. It's not bad by any stretch but if you want to get it better, you can get it better.

Few things I noticed on the slow mo:
Your off hand needs to come over a little bit more which will allow your lead hand to come up straight. Aligning your hips a little more to the left can help with that. You want your front foot, knee, elbow and shoulder all aligned to the ring and on the same plane.
Bit more knee bend.
You're reaching outwards more than upwards on your follow through, which makes it come out flatter than you'd want. The hip rotation should make you naturally lean back more and push upwards.
Pretty much what KET said

Overall, structurally there's not a whole lot going wrong there. Just needs some tweaking.

Firstly, thank you to everyone that replied!

Do you guys think the technique I linked below will help? Essentially your off hand points it's index finger to the sky resulting in no off hand effect on the ball. If I focus on this, follow through and bringing more power from my legs, do you believe this will help?

Link of the technique: https://youtu.be/T7kTJPnnoR4?t=244

I was expecting to see a White Zorro.

A couple of points I could see;
All of your shots start with the ball on your left hip. Try to bring the ball to your shooting hand, not your hand to the ball. It will make the upswing part more consistent.

Relax your hand on the follow through. Your fingers are really stiff. Try to get your hand to flop so that you get a nicer arc and spin on the ball.

Only minor points as the action itself is fine.

Above posters all make correct points so not going to repeat those.

The reason why your follow through is more horiztonal than vertical I think is because your using a lot of palm in your shot. I'd work on just making sure that your fingers are the last contact with the ball - and so you should be aiming to follow them right through so that they are pointing directly down;

In terms of drills to do this - grab a basketball and lie flat on your back and just practice shooting the ball with the fingers. Also before you start shooting, just warm up with 30 or so shots 2 foot from the basket with 1 hand (focusing on form and using fingers).
If that still doesn't work, you can get aids (e.g. foam balls that attach to your palm) that prevent you from palming the ball and force you to use your fingers.

In saying that though, as long as the shot goes in right?

It's funny because people always says Ray Allen has the best shooting form - he had good form but there was one glaring problem with his form - he brought the ball down to his groin every time before re-loading to shoot.
Of course it didn't matter because his release was still that quick it didn't affect him - but technically speaking.

For me, Klay Thompson has the best pure shooting form of all time - its beautifully simple;

Mate - those shorts are they Hobart Phoenix???

Have a bit to do with them

For some reason it posted under Anonymous but that is me! ^