I have ADHD, so I have many traits which make me not especially cool or consistent, and at least 2 of my 3 have ADHD, which makes their behaviour especially baffling/challenging. I only found out about my own ADHD when DS1 was 8, so I went through the worst of it where we clashed constantly without any idea why it was so hard. The younger two are 10/13 years younger than DS1, so I've done a single child and close in age siblings, essentially separately.
The youngest is weirdly the most active and won't sit still and needs to be on the go at all times but seems the least ADHD out of the three of them, in the fact that he actually has impulse control and can understand being told off and tries to follow rules and work things out and think them through. (The others have had very little of any of this).
Anyway there have been absolutely times where not much worked. A lot of my parenting has been extreme trial-and-error. I often felt I was firefighting, which is what I call the bit that you're doing. Like they're all over the place lighting metaphorical fires and all you can do is chase after them trying to put them out. You can't very well not put the fires out, but you know that putting the fires out is not solving the actual problem, and to make things worse now there's all this (metaphorical) smoke and broken stuff everywhere, which just makes it easier for them and harder for you.
I'm not saying the ADHD thing to diagnose anyone, because there can be other reasons that parenting is hard. I am just saying it to illustrate that there can be patterns which underlie everything which can be a sort of self-feeding cycle in that the traits in me which meant I was lurching from moment to moment trying to react also meant my children had more moments than most children and were less responsive to "standard" advice and also meant that I was missing certain steps of the "standard" advice which are obvious to everyone else (apparently) but are not stated so I didn't know I was missing them.
But also because everything was a disaster it kind of meant that I was trying to attack things at random, any time a "fire" broke out and realistically that wasn't making a dent in any of the more significant structural issues which were things like - our house was a tip, my default learned reaction was panic/irritation, we had no set structure to our day, the kids had too much screen time until I felt guilty and would pull the plug with little warning, bedtime would drag on so they were tired/our mornings started late, their toys were all shuffled up and mixed or bits lost etc, I was too burned out to play or give much positive attention, we often would not get dressed out of PJs, it was hard to leave the house, mealtimes were a bit of a disaster, I would let things go until they were a "fire" and then suddenly react (etc etc). So I often felt like things didn't work, but realistically - the advice was for someone who had their shit together and I really did not. You might not be as bad as I was, this is definitely describing me at my worst and it wasn't like this all day every day and TBF probably not all of these things at once but each of them has been an issue at least once.
The only thing that really helped was sticking to trying to solve one issue at a time and really making a very clear and consistent effort on that thing, understanding it wouldn't be perfect, understanding it wouldn't change immediately, understanding that other things would get in the way, but it was still worth persevering and making progress anyway. What I would advise my younger self would be to sit down, of an evening - use the time that they are asleep, and imagine that you were going to appear on a TV programme, maybe something like Supernanny.
You don't have to share it with anyone but if you look at your day to day life and imagine it through the lens of a TV programme, what would be the 3-4 issues that you'd expect the programme maker to focus on? Or if you could imagine say 2 things that you would love to wave a magic wand and change. Then try and think of ways that you could really set those specific things up for success and/or work on the skills associated with those things, and/or set up the environment or expectations in advance so that those things will work more effectively. And make that your highest priority over the next 2 weeks or so, as a sort of experiment. If you are too tired to do it now, make tomorrow an observation day instead and make notes throughout the day and then encapsulate it into a few things. See how it goes.