So it's the Google Play Store memory that "grows"?
An app using a lot of memory usually isn't an issue, memory is there to be used, and should be freed when other apps needs it, but if the device shouldn't "slow down".
Maybe the new billing API isn't the issue. You seem to be using the Automate accessibility service, try stopping any flows using it, e.g. the Interact block, and disable the accessibility service.
The other apps may not be using version 4 of the billing library yet, as Automate does, but it will be a requirement next year.
The other apps may also save/cache the "premium" status locally within the app, which is not advised since its easily "cracked", and Automate doesn't since users could easily use the app itself to copy/write the such a cached value.
Automate is also always running, which most apps doesn't do.