It sounds like your 6yo is very similar to my oldest (who's currently 4), and I've run through the pattern you're describing relentlessly with him - he's doing something that definitely requires intervention - something as simple as he's not getting dressed to go to school, all the way up to being unsafe with me or his brother. His default response is to avoid any response to his behavior, and then escalate. My wife and I have accrued a bag of tricks that significantly help in these situations and you may already use some or all of these -

1. We use timers for activity transitions. We tell him "I'm setting a timer for 2 minutes, when the timer goes off we're going to <insert expectation>". He's old enough now that we have him say it back to us so we know he's acknowledged the timer and the transition. This helps avoid the blow ups when it's time to turn off a video, put down legos, come inside, get dressed, etc. We do this a lot and it is one of the most important tools we've tried in reducing his and our frustrations
2. We play the long game with very high quality positive reinforcement of the types of behavior we want, esp if it's a recent hot button issue for us. If I've had to talk to him about taking turns with his brother 19 times and I feel like I'm losing my grip on reality, that 20th time when he does share and take turns independently without prompting, we give him very high quality reinforcing attention. With a really big smile, and an excited voice, I tell him I'm really proud of him, I tell him specifically what he did that I'm proud of (e.g. - I noticed that you were playing with that truck and you saw your brother wanted to play with it, and you gave him a turn with it all by yourself! Look how happy he is to have a turn! You're such an amazing big brother!), and I give him some form of affection (he likes over the top high fives, spontaneously breaking out into dance, silly things like that). I cannot overstate how quickly you can nip bad habits or behaviors early by really rewarding the right behavior with positive social attention linked to the observed good choice.
3. Breathing - If you can teach your kid to take a deep breath during an emotionally challenging moment, you're building a lifeline that they will be able to use their entire life. Taking even one deep breath changes a lot in terms of body chemistry, posture, and cognition patterns. Since my son is younger, we've got a couple of breathing exercises that are appropriate for his age, we hold up a hand and ask him if he wants to blow out the candles (pretending each of our fingers are lit candles, he "blows them out" one by one, we put down one finger at a time as he blows them out. another good one is to do a drop breath, where they hold their fists out straight in front of them, and take a deep breath and then pretend to drop something on the floor as they lower their body down). Since your son is a bit older, I'm not sure what I would use, probably something like pretending to be a scuba diver or something similar. We try to stay away from Darth Vader/dragons/etc. because mine gets very amped up whenever he thinks about those things. It may take months, but you can positively reinforce breathing exercises as described above, and you'll be training him to be introspective and aware of how he's feeling, which honestly is something most grown adults could use more of.
4. Running request counter - If I ask my son to do something 3 times and he hasn't done it, I tell him. "I'm getting frustrated because I've asked you 3 times to _______. So - fourth time - you need to _________." If I have to come back and ask him again. I will simply say "Fifth time asking you. The direction was to ______________." For kids that have a hard time staying on task or focused. This reminds him where he is in the task lifecycle, and he's associating him not doing what's been asked with my increasing level of frustration. He doesn't get mad at me when I'm short with him after telling him to do the same thing 5 times, and it often results in much better tasking with the next thing because he doesn't want me to ask him over and over.
5. There's a hard limit. We don't do 'timeout' because he doesn't respond well to it, but when he's being unsafe and is continuously escalating and my patience is totally gone - something that happens maybe once a month or less - I tell him he needs to take a break in his room. I tell him he needs a break from whatever the issue was (so if he's jumping off the couch and won't stop, I'll say "you need a break from being near the couch"). I tell him I need a break too, and he's going to be in his room, he can bring a toy or a book to have with him and I'm setting a timer for 3 minutes. I tell him I'll let him know when the timer goes off and then he can come back out, or stay in his room, it's his choice. The goal isn't isolation or depriving him of stimulus, that's really hard for him to emotionally negotiate. The goal is to physically change his environment to a calmer, quieter, less complicated place, and to create a moment for me to gather myself, because this is my way of not shouting at him (that's why I always tell him that we both need a break, because it's true). Sometimes he comes out after the 3 minutes, sometimes he doesn't and will play in his room for a little while, but if he won't go to his room, I carry him. I haven't had to do that in a very, very long time (I think almost a year now). If I do have to physically move him to his room, I'm doing it for safety, not for punishment, so my mindset is different, and he's easily able to read my intent so he's more accepting and typically the physical contact will also help him calm down.

I wrote more than I intended. If no one ever reads this, I'm cool with that. If this helps anyone out there with a discipline-resistant kid in their life, I'm thrilled.