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I just chatted with John about this question and need to correct his suggestion that perhaps support for older files has been dropped -- it has NOT!
I just opened a couple of vsd files using Visio Plan 2, which is a superset of Visio 2019, and it worked fine. Here's my version info:
Just after I typed the sentences above, it occurred to me that perhaps there is a difference between Visio 2019 and Visio Plan 2 for older files. I doubted that was the case but to prove the point, I fired up a VM with Visio 2019 and opened several vsd files without any problem. This is my version info:
It does look like my version of 2019 is newer than yours, so it would make sense to update your copy of Visio just to be sure.
Beyond that, try opening this file -- it's a dead simple flowchart -- to see what happens. If that opens and your files don't perhaps there's an issue with the files.