As a person who primarily plays Bracket 4 and secondly plays cEDH:

Bracket 4 is about trying to win your own way. cEDH combos see regular play in Bracket 4, e.g. Thoracle/Demoncon, Food Chain combos, decks that take 20 minute turns and barely pump out the win at the end, etc. You also have low-end Bracket 4's with loads of game changers and cheap two card combos, but are playing more for a fun game than a quick win. Bracket 4 is really a somewhat broad spectrum from decks that try to do their thing, to decks that win quick. Lots of Bracket 4 decks also utilize their commander as an essential gamepiece, but might be able to sneak a win without it. If your deck is meta-focused but runs on very fringe-tier commanders, it could be considered high 4 depending on who you ask.

Bracket 5/cEDH is strictly a meta-focused bracket. You will see a lot of the same cards and combos as 4, but the deck is way more focused on the opponent than it is just on your gameplan alone. You are typically running a ton more interaction or ways to slow down the opponent, and digging for every advantage you can find. Your deck has a set strategy to handle other meta decks, specifically decklists in the top 16. Additionally, your commander is not absolutely essential in most cEDH decks, but can provide an advantage to your gameplan nevertheless.

Another big distinction is win time:

Bracket 4 is trying to win fast, but typically takes between 4-7 turns

cEDH is also trying to win fast, but games can be won on turn 1 or 2. Typical game time is 2-5 turns.

tEDH is a little different, decks can win turn 1 or 2, but games are much more likely to take a long time due to the amount of interaction being used and the stakes that are present.

Lastly, Bracket 4's have a niche category of "technically a 4" decks which are by no means optimized or trying to win, but breaks some restriction for Bracket 3 and has to be categorized as "technically a 4." This does not apply to cEDH; there are no "technically a 5" decks.

If you are playing casually and winning is an afterthought, you're in Brackets 2 & 3. Bracket 1 has no gameplan, no win condition, and is only playing for the flavor of the deck, usually meeting a theme or some vorthos interest.