nonconfigure

Hi nonconfigure,
Short answer: yes, switching to the edge kernel is the right move, but here is what's actually going on so the fix is not mysterious next time.
Why the 6.1 vendor kernel cannot drive the fan. The Rockchip 6.1 BSP ships its own thermal driver tree (`drivers/thermal/rockchip_thermal.c` under `/proc/vendor-thermal` paths) and its own PWM fan driver, but it does not expose the standard `pwm-fan`/`thermal` cooler bindings that the mainline/edge driver expects. So even if a board file declares a fan PWM and a trip point, the vendor kernel will not actually wire them together — the cooler's `cur_state` stays zero, the PWM stays at 0% duty, and the fan looks dead. That's why another 5 V fan on the same header behaves the same.
Why edge kernel 6.19.6 fixes it. Mainline wired `pwm-fan` + `thermal` on the RK3588 about a year ago and the cooling-map bindings have been refined in edge since, including the `map0/map1/map2` node-name collision that defcom5 landed in Armbian 26.8 (PR #10514, merged Monday). After that fix, edge 6.19.6 on RK3588-class SoCs sees the cooler properly, and the trip points declared in the board DT become active.
If the edge kernel doesn't pick it up either, the next thing to check is the DTB. The CM3588 FriendlyElec build carries a vendor DTB which references the 5 V header as plain GPIO, not PWM. You can confirm with `ls /sys/class/thermal/` and `ls /sys/class/pwm/` — if the cooler is missing or the PWM chip is absent, that's the symptom. The fix is to overlay a DTB fragment that exposes pwm0 (or whichever PWM channel is wired to the FAN header on the NAS carrier) and bind it to a cooler with trip points at 60°C / 75°C / 85°C. There are CM3588 community overlays floating around for this if your vendor kernel doesn't have one — let me know and I'll dig up links.
A note from the other side of the same problem. We make an industrial RK3588 SBC (the EM3588) and we ship it fanless by design — the SoC + DRAM + PMIC envelope is rated for –40°C ~ +85°C at industrial temperature grades with a heatsink but no active cooling. In an enclosure at 30°C ambient the junction-to-ambient rise is what matters, not PWM. That's a different design trade from the CM3588 NAS form factor, but the engineering pattern is the same: most RK3588-class devices do not actually need a fan unless they're in a sealed box or running heavy NPU/GPU workloads continuously. If your case is open and the NAS is just acting as a NAS, you may be better off removing the fan entirely and letting the SoC thermally throttle on its own trip points, which the vendor kernel does correctly.
 

You are on a vendor kernel.  That is not mainline linux, you need to be on current or edge to run mainline.  Having said that, the general rule of thumb is that vendor is old (unpatched with all that implies security wise) but generally feature complete, while mainline is newer but waiting for features to be accepted in mainline (some of which might never get ported to mainline).  
Each user generally cares about different features, so try different kernels to find the kernel that works best for your use cases.