I took 3w vacation after recovering from covid (which also took 3w). I just couldn’t face the work. I’ve been back at work for 2w and I am highly inefficient.
Were you doing the work all day thing, then come home and tinker? That was my path to my worst burnout... I have to keep my coding under 40 hours...
When you say you are fighting fires outside of wrok hours, is that as part of an on-call schedule? If it isn't then you all collectively need to sort that out. You need a proper on-call schedule with strict rules about when things get escelated and to who.
You need to have time when you are genuinely not working, and not thinking about work. If there is always the potential for some crisis then you'll never switch off. Not being able to geniunely put work down for some of the time is a big part of burn-out. Combining it with a lack of any feeling of real accomplishment and you are on your way to a collapse.
If you are the only person who can deal with certain types of issues then you need to make it a project to train up more members of your team, that's good for you, it's good for them, and its good for the company. Make it officially part of your job, set targets and goals, get explicit buy-in from your boss/the company. Don't make it some amorphous, vague personal goal, make it concrete. Teaching people, helping them level-up, can be hugely rewarding work. I've had huge job satisfaction helping my more junior developer skill up over the last year. I get a lot of pleasure and reward out of seeing him knocking out great work, it's almost like vicareous job satisfaction and it means that even when I'm having a sluggish week good things are still happening that I'm part of.
I guess that is the core of the issue. I am never switched off of work, and it caught up with me. I am not sure is it just my personality.
Something I've found as I've got older is that I simply can't manage without good sleep the way I seemed to be able to when I was younger. My younger team member is in his mid 30s and we were talking about this last week. He'd been pulling all-nighters (he's working around homeschool too), and it had been affecting his work, stuff was getting done but it wasn't great, and he was useless the next day. He's been operating the same way he used to do in his 20s when he was doing a PhD and didn't have kids. I think I've finally convinced him that the price you pay later is almost never worth it, but it's taken him a while to admit he just can't maintain that level of effort.
Getting older sucks in a lot of ways, a lot of them are quite subtle and happen slowly. I think the ability to run at maximum effort for extended periods of time is one of the things that you lose to some extent. That isn't to say that younger people don't get burnt out, but I think we recover quicker when we are younger, a bit like how we physically heal faster.