First, I think it would be to your benefit to investigate whether this project of yours was even interesting to your grandparents. Youve shared your interpretation of the situation (they are practically homebound and may be missing out on some experience with the wider world), and it seems reasonable, but it does not account for their perspective. They may not be missing anything about the wider world. Or, maybe they are missing some aspect of it, but don't view "digital tourism" as a valid substitute. Most likely though, they're just pleased their grandchild is visiting and want to focus on that, rather than the TV or computer.

As an illustrative example, imagine an introvert and extrovert coworkers. The extrovert discovers the introvert has no weekend plans, and assumes that they must be lonely or sad. They, with the noblest of intentions, try to cajole their colleague into going out on Friday night. The introvert, who has been looking forward to finally being able to settle into their latest novel, is upset that the extrovert is projecting a void onto their lives that they don't see as a void at all.

I'm not saying that that is what's occurring here, and obviously you know your grandparents better than strangers on the internet, but I do think it's a possibility that should be investigated before you commit to any plan.

I think this depends a lot on the grandparents personality and mental state. If I had to do this with mine, I would pick places they have a personal connection to. For example, where they were born, the place their school is or used to be, somewhere memorable they visited during their honeymoon, you get the idea. Seeing stuff like that evolve through time is more interesting imo than just visiting, say, Paris or Tokyo virtually.

I don't know if any of the Google cardboard vr stuff works anymore but there where plenty of tours for different sights and areas.

if you're British, maps.nls.uk is fascinating for seeing places evolve over time