It is a subscription. It always has been a subscription:
""the action of making or agreeing to make an advance payment in order to receive or participate in something"
We have been purchasing VERSION subscriptions, lasting at least a year and often longer. X3 was a 16 month subscription and we received five "issues" (versions).
A subscription does not have to mean getting a new "issue" every month, week, or quarter.
Paying monthly does not make anything a subscription. It is a payment plan.
That I make monthly payments for my house mortgage does not make my house a subscription.
But if I do not pay a few payments, the functionality of the house will change to not-living-in-this-house mode.
Another year of payments and I will "own" it.
Then I will get a new mortgage to make improvements.