Creating a high quality game engine is by no means an easy task, but you don’t need each contributor to know all of these things and you can use existing libraries for a lot of them. A lot of the things you mention have good quality MIT-licensed (or similarly liberal license) libraries you can use to save time. Its still going to be hard, but its not thaaaaat inaccessible.

Some examples: for entitiy systems, EnTT is amazing. For a job system you’ve got stuff like cpp-taskflow, for physics there’s bullet, for graphics there’s bgfx or full blown renderers. Sure, these won’t solve all of your needs, but they’re a good starting point that frees you from having to do a lot of stuff yourself.