Hello @lettuce_unity ,
Yesterday we officially released IAP 2.2.0 on the Asset Store which includes Google Billing Library v3.0.1 and the migration / deprecation to Google AIDL.
Unity IAP package 4.12.2 is now available page-2#post-6506532
If you update today you will not have to worry about the headache of updating your apps before the deadline which will happen in 2021, when Google officially deprecates their Google AIDL services.
About the topic of SubscriptionManager, please refer to the post here: Google Play Billing v3 and SubscriptionManager - Unity Services - Unity Discussions