Can I use a 4b graphite pencil for regular drawing?

Why not try it and see whether it suits your particular needs?

Depends on the pressure you apply and how often you sharpen it and what style you are going for.
Do not let descriptions about what those pencils are good for stifle and restrict you. Just do what you think fits.

I have a bunch of drawings that I did that are too light imo. Every once in a while I grab one and attack it with charcoal. It’s like re-visiting the fun I had drawing it.

My point is: you can always go over your drawings later if you don’t like it.

I usually use 2B, but I also tend to be a bit heavy handed when I draw.

You can use anything you want to create art. 4B will give you an easy dark black. Borrow one from a friend or try it at the store. It’s your drawing.

Buy a complete set of pencils. Try them all.

See where things take you.

I use B for drawing outlines. Light strokes. You can erase it without leaving traces.
Then, I start shading darkest areas. Depends on picture, I use 7B. If you want dark most black, then probably go for charcoal.
4B and 3B or 2B for medium dark shades.
B pencils are dark shades and soft. H pencils are for lighter shades, and are hard and brittle; they leave a mark after erasing. So, I don’t start with that. For example, I use 2H for white parts of the eyes.

So, I would prefer B to start drawing outline instead of 4B.