Yeah, using a 9 year old work laptop as my home server.
Then with the surging energy prices last year I decided to switch out that laptop with a raspberry pi 4 as server.
Conclusion: I now have a laptop and a RPI running 24/7 🤦‍♂️
My RPi4s and 3s will out perform my older laptops, apart from the just retired P50 (gpu nearly died). That one is 6y, the others are 11y old HPs and a 16y 32 bit Xxodd (wierd brand). tje RPis are sufficient for normal server use, the nwew laptop (last gen i9 with 64G mem) can host (nested) kvm clients, so no need for extra hardware. (And still I save them, just in case ;) )
I'm glad I don't need computing power then. It just runs a webserver, 2 databases, mail environment, puppet master, icr client and some random stuff I just start and forget.
It does the trick here and it and it's predecessor Rpi3 and 2 managed, are quiet and enough for here. Both 3s boot from microsd and run from USB SSD for the OS, data is on nas. All are stock, no extentions, apart from an extra USB nic on my firewall. (Somehow having 2 different physical interfaces sounded preferable to me for a firewall)
The old 3s are now interface for my smart meter and a domoticz system.
BTW I see the Thinkcenter you mention for €250 online, My RPi4 cost me as kit €108 (8GB version). That was before all prizes went trough the roof though, as I see the separate board now for €125.