for the fireworks:

this article has some good maps on where to watch: MAP: Where to Watch the 2023 Fourth of July Fireworks Without Going to the National Mall - Washingtonian

What really determines where to watch is desired proximity, your tolerance for crowds, what buildings/memorials you want in your photos, and then security.

Regarding what's allowed on the Mall or other National Park Service areas: here is your definitive guide: Washington, DC, Fourth of July Celebration (U.S. National Park Service) (nps.gov)
Security on the Mall itself is pretty strict. In some other areas, not quite as diligent (particularly with alcohol, glass, and even grills).

In my opinion, the very best is actually on the mall - get there early to leisurely enjoy the Smithsonian FolkLife festival, then stay for the fireworks. Get the right position near the Wash Monument and they will seem to be in larger than life and 3D. The only thing better is watching from the White House or from a boat (either way, you will need to KNOW someone).

Being an Air Force brat, I have very much enjoyed watching from the Air Force Memorial - the AF Band performs with world class guests, the Honor Guard/Precision Drill Team performs, and you get a great view.

This year I watched from the "Mount Vernon Trail" / Columbia Island grass areas on the "Virginia side" of the river. The fireworks are big but you get all the iconic buildings in the background as well as watching all the boat activity. Easy access from Pentagon South Parking, easy walk to the waters edge, lots of space, lots of bathrooms and doesn't feel crowded.

For details on the concert on the Capitol steps: FAQs | A Capitol Fourth | PBS the show is produced by PBS and they control most stuff except the security - lots of info in those FAQs

But the most important tip, that you will only get from me, (at no extra charge!), is to plan to wait for an hour after the fireworks end, to begin to make your exit. The crowds which felt large but so spread out will all merge into the same few exit points, and Metro stops, and parking lots and highways/roads - it will take at least an hour to clear out and the highways will be clogged. So, prepare with enough food/drink for after the show, relax, and get home just as quickly as if you threw yourself into the maelstrom to hurry up and wait immediately after the show.

And finally.... a whole bunch of photos from various vantage points: Photos and Multimedia - Washington, DC, Fourth of July Celebration (U.S. National Park Service) (nps.gov)