When updated to macOS High Sierra, then received message "App is not optimized for your Mac". This pertains to HRBlock tax preparation software, and the change from 32 bit apps to 64 bit apps. Question : will HRBlock provide the necessary updates to access past returns?
MacBook Pro (Retina, 15-inch, Mid 2015), macOS High Sierra (10.13.5)
You'll have to ask H&R Block that. It's not something Apple has anything to do with.
Since the next version of macOS 10.14, Mojave, will still run 32 bit apps you should be good for at least about 18 months.
Does the software not allow you to export the whole return as PDF? If not, that sounds like a good reason to switch to another Tax prep software.
But, as OT stated, there isn't anything to worry about for the near future. H&R Block would have to answer your original question. The fact that they haven't written a 64-bit app in 12 years seems to suggest another reason to switch software vendors.
When will HRBlock provide the necessary updates to open previous years tax returns?
