More Windows computers have Thunderbolt built in now, especially laptops, but the extra expense for a Thunderbolt enclosure and cable isn’t necessary for this. USB 3 is fine. (Also, for future computer purchases, keep in mind that USB 4 and Thunderbolt 4 are the same, so if your next computer has USB 4 ports you’ll be ready for anything.)
For me, a USB 3 external SSD works fine. Aim for 10Gb/sec USB 3, although the older 5Gb/sec might be OK on a budget. And definitely not the very old 480Mb/sec USB 2. Today, 10Gb/sec USB 3 is common and very affordable.
A quick and easy solution is a tiny bus-powered USB 3 SSD like a Crucial X series or Samsung T series, both widely used by photo/video pros. As a Photoshop scratch disk, you might not need more than 1TB.
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