This is a Drupal 8 (should work on 9, too) module that can be placed in the /modules/contrib folder and installed like other modules.
Unlock Protocol provides the ability to show/hide content based on whether the content has been "unlocked" by a payment with digital currency. This payment uses a browser-based extension wallet, and hence a "subscription" can be determined.
The premium content is simply hidden and shown in the DOM in this module, illustrating the capabilities.
Visit the Unlock Website for more details.
Use the Unlock Protocol's website to create a lock. Look for the dashboard link. Once created, copy the address to the lock, it will start with 0x… and look like a random hash.
Have an admin enter the lock address in the Unlock settings page
Add premium content blocks using the provided custom block type. Structure » Block layout » Add custom block. Choose Unlock Premium Content.
Add the button to subscribe, usually below or above the premium content. This is a custom block. Unlike the provided custom block type, this block is added by: Structure » Block layout. Find the appropriate region and click Place block. It's called "Unlock button block"
Premium blocks will hide/show based on the user's subscription status.
Check the console if there seems to be trouble.
These instructions are also available in the module's help page.