I recently got bussy making some blocks by copy edit concrete blocks and placed them in my resourcepack and I also made some by using blockbench.
But the blocks wont be available in game i possibly need to register them in some file but i cant seem to find it also im not sure how to google this since I dont know if it is made with a resourcepack/behaviorpack/mod or addon.
So in short I have some custom blocks I want in game but im not sure how or where to find some good information on how to do it other then itemframes and commandblocks.
According to me you can add these blocks into the game with the help of modifications. As you know without modification its impossible for your to add blocks. But as per my opinion you should discuss with one of the game developer and create a good addons. In this way might be you get some help.