I used to think a lot about up-gradability before but often find that when a cpu is too slow then it is also so old that I have to change the motherboard and ram too for compatibility reasons.
Same thing with the motherboard, if it fails I’ve never had it be new enough that I can bring my cpu and ram with me to my next motherboard (unless buying an older motherboard second hand).
And many of my disks will be old enough that I want to replace them too, at least if they have anything important on them.

Only things I’ve brought with me when upgrading desktops have been my case (including fans), psu, gpu and (some) disks.
Having a quiet and dust proof case that is easy to build in and a good psu that https://cultists.network/140/psu-tier-list/ endorses has become higher priority to me since then, as I know they might last me more than one build.

as a senior developer my advice is: buy parts and learn to assemble, the exchangeable parts are (at least for me):

• CPU/Mainboard/RAM : always bought as a bundle (RAM at least 32GB), because dependencies are too high, I prefer AMD, but ymmv
• GPU : Easy to switch, easy to spend a fortune, i always prefer mid range cards or older ones like the AMD RX 6600
• Storage: Always the fastest possible, if you need to go cheap, then make it smaller, linux does need no significant space, and i run my system on a 240GB M.2
• Case/PSU: Buy it only once, i still use a case from the 90`s, the PSU will only be upgraded if connectors change, 750W are enough for most of the work
• HID: Dont go cheap on Monitors and Mouse/Keyboard, IPS displays are a must, if you have multiple screens (angular view is distorted otherwise), Most gaming input devices work very good for programmers, i prefer logitech (with ratbag), but corsair has very goot support under linux too (ckb-next)

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