I've often struggled with understanding if I'm working out right. I find it hard to tell when I'm working out if my form is absolutely correct. And there's only so much you can glean from youtube videos.
Are there any apps with a checklist of form exercises and/or a heatmap diagram indicating where I should be feeling the pressure for a given exercise?
How do you know if you're working out right?
There are a couple of things to consider when answering your question. First, have you given any thought as to what your fitness/training goals might be? Determining if your training is effective should be related to what it is you are trying to achieve. Setting short term and long term goals should help decide if you're training correctly. Over time, you'll be able to determine if your training protocol is effective in attaining those goals.
Secondly, while using video sites for training info can be helpful, it lacks a feedback loop. Consider working with a CPT (Certified Personal Trainer), or, someone who has advanced experience and can guide you.
You probably imagine "working out correctly" to involve
(1) is very important, and it sounds like you are already doing as much as you individually can. The only next steps you could take would be to ask other people to assess your form. If you don't know any experts in real life, you could film yourself and post it in reddit communities (or other bodybuilding/fitness forums), asking for form critique. Perhaps this community is also an option for that, although I'm not sure if such questions would be on topic; perhaps you can ask on the meta.
(2) is actually largely a myth; as long as your body goes through the correct motion, the exercise will be effective. The only way to nitpick your way through to improving (2) is through repeated practice and experimentation; try a slightly different joint angle, slightly different range of motion, etc., and pay attention to how it feels. It can be quite fun to do this, and may come with a placebo effect, but has been shown to actually not matter very much.
As long as the weight is low, it's quite hard to work out incorrectly. Especially since you yourself are so conscious of this. Just make sure you don't jump yourself into the deep end of doing anything too heavy too soon.
You said in a comment
When working out, I feel like you have to rely on your own instincts to make sure you're doing it right. There's no "calculator" equivalent
The calculator is: avoiding pain (which is your body telling you something is wrong) and tracking progress. As long as you are making progress, and not feeling pain or twinges, your form can be considered "correct". There's a lot of leeway within these parameters, and that's where instincts come into it. Your own fitness journey will show you what works best for yourself.
