Mac computers based on Intel processors are obsolete now. Here's a list of what not to buy and why.
TL:DR — Apple no longer make Intel-based Mac computers. With the introduction of Apple silicon these computers are obsolete.
It's not just me, heres what the Macrumors website says about the last of the line Intel-based Mac mini — "The Intel-based Mac mini is a relic from the period before Apple began to transition the Mac lineup to its own custom silicon, which offers massive performance and efficiency benefits. For this reason, and since it is effectively four years old, those interested in the high-end Intel Mac mini should not buy it under almost any circumstances." Tuesday August 23, 2022 8:00 am PDT by Hartley Charlton in MacRumors
Contents
KKPCW, CC BY-SA 4.0, via Wikimedia Commons
Mac Pro (2019), A1991, A2304 (MacPro7,1)
Apple introduced the 'new' Intel Mac Pro in 2019. It is supported no longer available new. It has the T2 security chip required for macOS Ventura and a wide variety of possible build to order configurations. It is obsolete - Mac computers with Apple silicon are more power efficient and more powerful. These are still great to run Windows or other Intel based virtual machines. You can't run Intel based virtual machines on Mac computers with Apple Silicon. Unless you specifically need Intel virtualisation or have software dependenices that require an Intel processor or a specific expansion card then don't buy one.
These are not really on the used market in volume yet.

Uadro, CC BY-SA 4.0, via Wikimedia Commons
Mac Pro (2013), A1481 (MacPro6,1)
Apple introduced the cylinder Mac Pro in 2013. It is supported but is obsolete now having been discontinued in 2019. It doesn't have the T2 security chip required for macOS Ventura and it doesn't have USB-C and while it has ample ports including dual Ethernet, HDMI and 4 USB it only has Thunderbolt 2 although it has 6 of them. If you have these then macOS Monterey is the last official macOS for them so it is time to start to plan to replace them. These are still great to run Windows or other Intel based virtual machines. You can't run Intel based virtual machines on Mac computers with Apple Silicon. I finally sold my Mac Pro (2013) in 2023. It ran for ten years almost 24x7 but does not have to expansion capabilities or ports to deal with modern peripherals.
Still want one?

Zach Vega, CC BY-SA 4.0, via Wikimedia Commons
All older Intel based Mac Pro and Xserve(MacPro5,1), (Xserve3,1),(Xserve2,1), (Xserve1,1)
All these older computers are obsolete now. Collectors still love them and there are utilities to help them boot macOS versions later than those that are supported but unless this is a hobby it no longer makes much sense to persevere with them. I finally decomissioned my Apple Xserves in 2022. Not a bad run for a line of computers discontinued in 2009.
Still want one?

Khaosaming, CC BY 4.0, via Wikimedia Commons
Mac Mini (2018)A1993 (Macmini8,1)
Apple introduced the Mac Mini (2018) in October 2018 and it is no longer available new. It is supported. It has the T2 security chip required for macOS Ventura and was available in a wide variety of possible build to order configurations. It is obsolete though. Mac computers with Apple silicon are more power efficient and more powerful. Unless you specifically need Intel virtualisation then don't buy one. If you do buy one try to get an i7 with as much memory and storage as your budget allows. It will hold its value better. These are still great to run Windows or other Intel based virtual machines. You can't run Intel based virtual machines on Mac computers with Apple Silicon.
Still want one?

Ashley Pomeroy, CC BY-SA 4.0, via Wikimedia Commons
All older Mac Mini's (Mac Mini 7,1 and older)
All the older Mac Mini's are obsolete now. The 2014 models can run macOS Monterey. You have to go back to 2012 to find one with a built in optical drive and firewire. Unless you really need that connectivity theres not much that these are useful for now. Even older ones are so slow now as to be unusable. There are a lot for sale at the usual outlets. Avoid.
Still want one?