I had 3 bikes, 2 of them did around 10k, 3rd one, well, I bought it at start of pandemic, then we moved WfH so it did much less.
Around 20% was riding around local forests, rest in city.
The first bike was literally like $300 (...probably closer to $400 now with inflation and all). I only replaced the saddle for more comfortable one but that's all. No disc brakes, literally the fanciest thing on it was that it had shocks on front.
But after finding job in big city and moving there I was using it for commute every day so after few years I decided "well, might as well buy something nice", bought one for I think like $2000, nice disc brakes, rear shock, lighter, "good" etc.
Comparing those two I went from mechanical rim brakes to hydraulic disk brakes and they did feel nicer, but in the end the rim brakes stopping power was just fine, it didn't feel as that much of an upgrade. Sure, a bit lighter to use but I could still yeet myself thru the front tire on rim brakes (probably). And rear wheel disc brake was entirely a waste, there is way less braking force needed on rear to lock up wheel.
In general I liked it but managed to break the frame (I was on max range of weight for that bike which probably didn't help), and decided to get something slighty cheaper, no rear shock (not much use for what I drive), cheaper accessories etc. (think it was about $1000). After a bit of riding turned out that only thing I missed was that tiny screw to adjust preload on brakes as the pads wear out. Drove few K so far, think some bearing in pedal broke (it's a bit wobbly), but not annoying enough yet for me to fix it.
In every case I had to replace sprockets as they use, replace the saddle for more comfortable one and install some accessory bits, replace the handlebars for one that fit me better and few smaller bit. But even the cheapo was reliable enough.
Generally the thing worth investing most is frame (as that will not change) and derailleur, as that will generally stay, brakes depending on riding (as I said, people driving hard off hills will probably have different needs than me driving some random forest dirt roads). Everything else you probably want to fit to your needs and you want to drive the bike for a bit to know exactly what you want.