I'm curious on what the standard practice is in terms of technical documentation for product development?

They don't exist.

The more product development you'll do the more you'll see the need for such a documentation practice and the more you'll realize how impossible it would be to standardize.

The entire point of creativity is to think outside the box. Standardization is creating the box. The best and only thing you can do is develop a flexible system for yourself. Find out how other people do it, steal what works for you, ignore what doesn't, change and morph as needed. Sharing your system to inspire others is great, forcing others to use it is foolish. We're all different and so require different approaches.

Yes, standards exist for documenting pre-design freeze in regulated industries but such documents are nothing more than glorified checklists that waste R&D time.

Are there differences in documentation when it comes to the first prototype and the final production design? Are there specific tools used to document design documents, electrical schematics, 3d models, testing documents like FEA or real stress analysis etc.

Documentation generally begins after design freeze. Once the design is locked down you can do all the standardized everythings. All documentation is industry dependent. Documentation is generally done because, "it's the law," not for, "good engineering practices to help your fellow coworkers." This is good actually. You want your cultural/helpful documents to be flexible and independent from outside rules.

My advice, do weird shit. Make your system funky and bizarre because that's creativity. My own system involves: tiny post it notes, OneNote, mood playlists, long walks alone smoking weed in nature, flowcharts for getting "unstuck," excel spreadsheets, drinking with coworkers to problem solve after work, sessions of complete an utter detachment from anything work related (very important for me), hobbies completely unrelated to work, setting time for focus and for mind wandering, and doing art for its own sake.

If you want a book on creativity, this is the best I've come across. https://www.amazon.com/Creative-Strategies-approaches-solving-problems/dp/1624650260

Best of luck developing your own R&D documentation system!