External SSD between Mac and PC

I don't want to get involved in a Windows-MAC flame throwing debate. However, you have to decide how difficult it would be for you to work across platforms; you have to decide whether the benefits outweigh the disadvantages. And your last sentence where you want the ability to process while traveling on the laptop does not imply that it has to be a Mac. A Windows machine meets that goal, as does a MAC laptop. 

The SSD should be formatted as ExFAT. Both Windows and macOS can read/write that file system. 

(I think Macs can read NTFS, but writing it requires third-party software. If the SSD was to be used only with Apple devices, APFS would be strongly preferred.)

That’s the volume formatting side to the question, at the OS level. The other side is what will happen at the application level, with Lightroom Classic catalogs. For that, you might want to watch the following video by Terry White, who works for Adobe. He shows how to do pretty much what you are asking: He has a Samsung external T-series SSD, a Windows 11 laptop, and a Mac.

As for whether you should add a Mac Studio to use with your PC laptop, it does introduce cross-platform complications, but it can work if you’re curious enough about Macs and open-minded enough to learn and resolve the platform differences.

The base Mac Studio is a great photo editing desktop (fast with a good GPU for Adobe applications). The Mac Studio specs are well above the Mac mini or iMac desktops, especially for the GPU. But if you’re very comfortable with PCs, it may be possible to build a PC desktop that runs as fast or better, for less money, and sticking to one consistent platform. And I’m saying that as someone who is Mac all the way.