We have a custom object that has a lookup to account (similar to Contact looking up to Account). We want the user who owns an account to see the records looking up to that account automatically without any user/admin intervention. The functionality would be similar to sharing setting "Controlled by parent". However, custom objects do not have this option. We want to replicate this option for custom object.
Other solution I have looked at is using criteria-based or owner-based sharing. However, that does not allow dynamic sharing (i.e., share with owner of the account) and is limited to sharing with previously described roles and groups, etc.
We want to make sure that the users can see the record as the new records are created with zero manual work. (e.g., Apex Trigger, Apex Class). This solution needs to be scalable with hundreds of thousands of records so manual sharing will not work and groups, roles, permissions sets may not be ideal.