Right now, no. The game should be available to purchase on Steam in 2026.
For this Subscribestar error, have you tried to directly register your card on your Subscribestar account settings, under Billing Info ? I had the same problem but i managed to fix it by doing this.
Unfortunately i have no idea on how to fix it. You could try to contact Subscribestar support, they'll probably have a solution.
Update : I found a possible solution on Reddit, people who had the same problem could fix it by switching from their country to US when they were trying to pay, you could try.