If this was right after one of the sales they ran last year, they had so many new users the support got very back logged. Not an excuse but just saying that's not the normal response time from what I have seen on here.
Is it still showing screenshots from the old UI? Not everything may have been updated for that. Also the path is different depending on if you have Hub Protect or not, you do not need a migration backup if you already have Hub Protect cloud backups (they are the same thing).
You can transfer: NEW! Transfer active subscription(s) from one hub to another
If you have Hub Protect already, then you do not need to use the special "migration" backup system. Keep your subscription on the old hub until migration is confirmed. Do a normal cloud backup on the source hub, then log in to the same account on the new hub and restore from the cloud backup. Once complete and confirmed you can transfer the subscription if the old hub is being decommissioned.
*I think some C5 models the Z-wave radio cannot be migrated (may be noted in docs). I think it was mainly models with a European external z-wave radio if my memory is correct (or was that only the C4?).
*I know that staff already said they were working on a C8 -> C8Pro migration feature, I think this is only for people without Hub Protect since if you already have cloud backups it should just transfer over with that.