The other responses go over the procedure for TPOD handoff and manual tracking, which is good to know but didn’t actually answer your specific question.
The reason your maverick didn’t release is because it isn’t locked on to anything. No lock, no release. When you designate a target with the TPOD, the maverick may fail to get acquire a lock. When the maverick has a lock on a target, the tracking gate (crosshairs) close. In the picture you provided, the crosshairs are still open. The easiest/quickest remedy is to hit TMS up with the maverick screen SOI to attempt a lock, as skywalker22 shows in his video. Sometimes it takes several attempts, especially if you are at 5nm or more.
Below are examples of an unlocked and locked maverick screen (taken from Chuck’s guide). You can also see this in skywalker22’s video. Note how the crosshair closes the gap once it acquired a lock.
