I've been running Catalina on my MP (late-2013 model) with no issues. My catalogs are substantially larger btw.
XMP - you don't mention the specific version of Classic, but I'm 99% sure yes (I do this with Clients on older versions)
Easiest way to be 100% in your situation is, of...
I-See-Light is entirely correct. It makes no difference that your system is set to open these in Ps, most of us set this to Preview, but it doesn't affect what goes on in Lr.
Lr cannot change files from JPG to XMP. XMP is simply a sidecar file as stated, written on demand from some programs...
Unfortunately, it seems the graphics card is below the minimum spec to run the current version of Classic. It's an old card (7 years) and seems to come with 1Gb RAM. Classic requires a minimum of 2Gb to display (more to actually use for processing in Develop)
Classic 7.x would run on 1Gb GPU...
To clarify, have you tried switching off the GPU in Lightroom? What's it set to currently? Preferences > Performance > Use Graphics Processor - set to Off. It's only used to assist in graphics processing and will normally be set off if Lr doesn't think it can use it.
Which model of graphics...
What are your Standard Previews set to (size)? Generally Auto is good. By the sound of it they aren't sufficient for Lr to use. Check page 503 in your Classic book (2nd Edition) for the loading logic.
Smart Previews are used in Develop, not in Library views, unless Lr sees the photo as missing.
Adobe don't have a check that specifies a catalog must be tied to an account, so short answer is you can use the catalog with either subscription. However, if it's synced to the cloud, then it can only be synced on one subscription (so the other computer with a different sub can still use it...
Page 442 of your Classic book (2nd Edition) point 4 (in the question about moving to another disk):
Open Lightroom and right-click on the parent folder. Select Find Missing Folder or Update Folder Location from the list, depending on which option is available. Navigate to the new location and...
I'd suggest put in a bug to the Adobe forum. It sounds very similar to a couple of other bugs (Quick Collection Custom Sort Order, email from LrC) that we have links to on our LrC 10.0 post.
No, 8Gb, and the original 128Gb disk. I so wish I could tell you something that jumps out as obvious! But it's an out of the box MBP (with replaced OS over time of course!) It's the 13" one.
Happy to check anything else on it to compare of course.
So, you have the photos downloaded now to your local computer? Depending on the size, you may be able to select them, right-click and compress then email. However, if too big fir email, then we often use WeTransfer (it's free and you simply upload to it and the recipient gets a download link).
I appreciate this isn't that helpful, but I'm also running a mid-2012 MBP without issues (it's as fast as I'd expect for the age of machine, 9 seconds to load Lr to the point of asking which catalog, then 15 seconds to load it). I mention it to give hope!
Tried uninstalling / reinstalling Lr...