Retention of transaction log if secondary replica is down in SQL Server Always On Availability group

Hi,

We have SQL Server 2017 Always On setup (1 primary replica and 1 secondary replica)

So far I understand primary replica send transaction log record to secondary replica and applied there. If secondary replica is down and does not get up for many days (for example 7/8 days) then for many days the transaction log will be kept in primary replica. Or transaction log will be discarded/truncated after certain time?

I need to know what is retention of transaction log in primary replica if secondary replica is down?

Regards

Arif