I am using Windows 7 on my desktop and I was wondering if Calibre 3.48 is the last version that will work with that version.

Thank you,
Shykat
Officially, 3.48 is the last version guaranteed compatible with Windows 7.

Unofficially: Some people have had success running newer versions, but it's not a given considering the version of Qt used isn't really compatible. And Calibre 5.x installer will fail outright for Win 7 though, so you'd need to extract the MSI.
No, that's 4.23, though if you have issues, go back to 3.48 which is guaranteed to work.
Thank you. I may stay with my current 2.61 as it does what I need it to.

Shykat
Did you miss the "free update to Windows 10" window? Support for Windows 7 ended mid January 2020, your OS is a big security risk.
Actually, you can still get Windows 10 for free. Here's the URL for a free legitimate Windows 10 upgrade.

https://www.microsoft.com/en-us/software-download/windows10?ranMID=24542&ranEAID=0JlRymcP1YU&ranSite ID=0JlRymcP1YU-jrNVQ1h2C6psPvkoOG4DMw&epi=0JlRymcP1YU-jrNVQ1h2C6psPvkoOG4DMw&irgwc=1&OCID=AID2000142_aff _7593_1243925&tduid=%28ir__2nidyfzsmgkfqj1hkk0sohz 3132xpsqk2xi0oxlf00%29%287593%29%281243925%29%280J lRymcP1YU-jrNVQ1h2C6psPvkoOG4DMw%29%28%29&irclickid=_2nidyfz smgkfqj1hkk0sohz3132xpsqk2xi0oxlf00
Are you sure? That looks like it just downloads the upgrade tool. It probably checks the versions and licenses before continuing. Have you run it recently on a Windows 7 machine?
I did something similar last December when I had to rebuild a machine from bare iron. I built windows installation media as described above, putting it on a USB stick, then ran it. When install asked for the product key I entered the original Win7 key. It happily took that and activated the machine.
Yes, I am sure. It's still free with this loophole. But make sure you have the key for your Windows 7 just in case you need it.
If you had already updated a machine with that key, it is probably registered. But, somewhere else has implied that MS are fairly lenient with this rule. I think it is to their benefit to let as many systems update as possible.