Checkpoint

make sure database is hardened (before syncronizing with always on f.i. )

use a checkpoint

One important thing to note here is that SQL Server can only truncate up to the oldest open transaction. Therefore, if you are not seeing the expected relief from a checkpoint, it could very well be that someone forgot to commit or rollback their transaction. It is very important to finalize all transactions as soon as possible.

sometimes , using several checkpoints after each other can solve the issue