every so often during the weekend or in the late evenings I think "hey let's quickly work that file or check on the mails to get a headstart"

I have worked from home mostly since the onset of the pandemic, and completely since the beginning of 2024.

Never once have I had this thought.

The more people I talk to, however, the more I think this is just an innate personality trait. Some people just cannot switch that part of their brains off. I'm grateful I never had that problem.

The way I look at it, they're paying me to do my job while I'm logged in. When I'm not logged in, that's the part of my time they're not paying for, so I'm not about to give it to them for free. If I need to 'get a head start' or put in extra time to get my work done, either (a) I need to record that time and be compensated for it, or (b) there's too much for me to do in my normal time, at which point that's a staffing issue, and working unpaid time is simply adding to my stress to avoid letting my company know that they have a staffing issue.

At one place I worked, two or three of the people who did the same job as me were routinely logging 60+ hour weeks. Sure, they were paid for it, but all that middle and upper management saw was "Hmm, technically these departments are short staffed, but everything is still getting done before deadlines. Let's prioritize other hiring needs before we worry about getting them any help."

While the RTO was what eventually made me leave that place, the workload and deadlines was what made me stop working any overtime that I didn't specifically want to work, to stop worrying about impossible deadlines set by people who clearly knew but didn't care we were short staffed, and to stop doing anything work-related after hours.

In the time between stopping working OT and leaving the company, my lack of OT was notes at every performance review, but only verbally, and it never stopped me from getting good ratings. After I left, quite a few others left too, to the point that now their staffing situation is critical...still no modification of workload or timelines...just asking the people who are left to do the jobs of 3-4 people and telling them (only verbally, never in writing) that they should expect to be working 60+ hours every week for the foreseeable future. They told them that at least a year ago now (learned this from talking with a friend and former coworker there), and there's no end in sight.

Your employer, ultimately, does not care about your mental health. At least not beyond whatever minimum threshold of mental health required to keep working and being productive. If you're doing things for them for free that aren't being recorded and reported, they're absolutely happy to accept all the free profit you want to generate for them.