Tl;dr: Blue collar jobs are often as mentally taxing as they are physically taxing, in my experience, whereas office jobs are mentally taxing but almost never physically taxing, and I wish more white collar workers would at least acknowledge that.

I'll give my perspective, as someone who went from an office job back to blue collar work, along with my dad's. My dad has been a machinist for almost 50 years, and about 15 years ago moved into a more hybrid role of actual work and managerial work. He would come home from work and tell us how exhausted he was, not from the physical work, but from the mental focus his new duties required. He only has a high school education, so he'd enlist me to help him write and edit his reports (and still does, if I'm available). He still says the mental aspect is exhausting.

On the flip side, I had an office job in the military, and while there were days where I was mentally exhausted, it always bugged me how a lot of people look at blue collar work as just physical. I could get home and still have the physical energy to go out drinking or whatever, or actually do my hobbies after work. When I got out of the military, I went back to the only other job I knew: cooking.

"Oh, it's just flipping burgers, it must be nice to just zone out, despite it being physical work." Yeah, that's why I have to mentally track each order, each burger, how long it needs to cook, communicating with the rest of the staff on the fly to ensure all 6 different orders go out at the same time, knowing what allergies (mentally) mean what food/ingredients need to be left out, understanding all of the food safety laws around professional kitchens, all while being able to communicate with employees who may not even speak my language to ensure we're all safe in a hallway surrounded by burning things and hot oils, with management breathing down your neck constantly that "customer 4 says their burger is still pink, they wanted it medium rare, why didn't you know they actually wanted it medium well?!" Plus being able to regularly lift 50+ lbs throughout the shift to restock ingredients, planning the 2 hours you have between rushes down to the minute with the rest of the staff to ensure you'll have everything for the next rush or it'll all fall apart.

Same with construction, yeah, some of those guys just pick things up and put them down, but do you know by feel and experience how tightly packed dirt needs to be before you can put asphalt on it? How to ensure the slope and grade run properly to ensure drainage on that new road? How long you've got from when the cement truck arrives to when the concrete is poured to when it'll set to ensure you've got the level or flat surface you need? Do you know the proper gauges of wire an electrician needs to properly wire new lighting from the breaker to that new addition you bad built? The different types of PVC piping needed and how to properly seal/bend/weld/etc to set up a house?

I work as a woodworker/general contractor now, and while I'm physically moving a lot of heavy materials, I'm also constantly doing math (algebra, geometry, and referential), constantly needing to plan out the steps to go from sheets of plywood to fully finished cabinet (when to cut, when to assemble, when to sand, when to stain, and if the order is done wrong, you've made your life hell or wasted the last 8+ hours of your work and now need to explain to the boss why you just wasted $300+ of materials because you forgot to sand the interior before applying the stain). Knowing you can't often just screw a cabinet to the wall, it needs to be laid out centered to the rest of the stuff that won't be installed until after you're done, it needs to be shimmed both along the ground and along the wall to remain square and plumb, the cabinet doors need to overlay by 1/2", the handles need to be exactly square and plumb to each other because even being 1/8" off will be obvious to the human eye.

This isn't a shot against anyone or their jobs: they're all difficult, in their own ways, and all require energy and mental efforts I'm sure all of us would prefer to spend elsewhere in our lives. But, I just wanted to point out that blue collar jobs aren't just breaking your back, they're breaking your back while racking your brain for 8-10-12 hours per day.

Blue collar jobs are often as mentally taxing as they are physically taxing, and at least in my experience from my time in the military, my office work was often mentally tasking, but almost never physically taxing.