It's worth noting that it's going to be easy to spend more money on supplemental equipment to drive this monitor than you would on a brand new display (which won't have ~10-12 years on the clock). This will become more and more true the more hacks you do to try to make it work. Someone in one of your previous threads about this display mentioned the Mac Pro 5,1 and some PC-brand ThunderBolt "cards" for example, which will cost you more in time alone than a brand new decent 27" display.
If you want a monitor to run on a PowerPC Mac or on an OS 9 computer, just go buy a 24-inch 1920x1200 business LCD like the Dell U2412M. (But there's literally hundreds of models in this segment, they're essentially fungible so don't stress buying a specific year's sub-model too hard.)
If you're looking for a "modern Mac" (whether to use with this display or just in general) honestly your money's best spent on an M1 Mac. Most Intel Macs that cost less than M1s do are outperformed thoroughly by the M1 and are at the tail end of their lifespans, whereas an M1 will be at the start of its service life.
I make the "haha a 2011 Mac is older than a Quadra was when we started the MLA" comparison a lot but a thing that's different is that new Macs tend to cost a bit less today than they did in 2001/2002, and because we're at the start of a Platform Transition, you get a
lot for your "cheapest available Mac, slowest that will ever exist on the new platform" dollar.
So what machine from the compatible Thunderbolt era should I be looking for to drive it, once tested?
For the
ThunderBolt display (not the LED Cinema, they're different monitors even though they look identical) 2011 and newer is the absolute minimum, and for all intents and purposes,
ONLY computers with Thunderbolt can do it.
All Macs 2011 and newer minus the Mac Pro 5,1 and the 2015-17 12-inch MacBooks can do this, but there's also lots of PC hardware with ThunderBolt and the display should work with
the TB2<>TB3 adapter. Minimum OS for that era will be 10.6 for the 2011 Macs, 10.7 for the 2012s, so-on and so-forth.
Absolutely nothing from the PPC era will drive this monitor, owing mainly to incompatible interfaces. (Midrange G5 graphics will happily output 2560x1440 to dual-link DVI, provided you have a good enough cable and your monitor supports that input, which not all modern 27s do, so you have to consult the spec sheets.)
As much as it pains me to suggest this I wonder what your prospects for installing Windows 10 on that laptop would be, if you can actually get it to work. 2011-era machines still support "Bootcamp", right?
I can confirm this works well, Windows 10 supports that machine well and it works fine, even without toying too much with BootCamp drivers, although if you decide to bother with that you can probably get some more mileage out of it as a portable machine, some better functionality of the function keys on the top row, the trackpad'll likely work better, etc etc.
In general, as a "modern computer" - Windows or Linux is the best way forward for these machines, which are rapidly approaching twelve years old.
That said: the 2011 Macs also run Catalina fine with the dosdude1 patcher, although we are now to the point where 2015 Macs are absolutely plummeting so if you're (anyone) hard up for a modern Mac, consider just buying a 2015 or newer. (Though: Catalina only has one more year of security updates, and I don't know how well OpenCore patched Big Sur or Monterey work on these almost-twelve-year-old machines.)
You can buy newer Macs, but the problem is that 2015 MacBook Pros (just as one example) are still fetching 400-600 and by the time you're paying $600 for a 7 year old computer with a 9 year old processor in it, you may as well consider budgeting $900 for a MacBook Air (they're on sale regularly) and getting a machine up front with ~8-10 years of life in it. Also, since you're workshopping using it with a 27-inch display, it's worth mentioning the M1 Mac mini - you can get an M1 mac mini for $600.
2014 Mac minis may be worth looking at, those can run the nwest OS (because Apple sold them into mid-2018 or so) and you can get midrange 2014 mini configs for
~200 (2.6 i5 8/256). The base 1.4GHz 4/500 config will probably cost a lot less and you can swap the hard disk for an SSD to offset the low RAM.
The 2012s have more internal flexibility but I'd say skip them (again, in the context of wanting a "modern" mac) because they've already seen their newest official OS version They'll run Big Sur and probably Monterey fine with patchers, but it's annoying to do. You can get the '14 with 16 gigs of RAM and dual storage if that's an important config.
Though, again, there's PCs with thunderbolt too.