This new system is kinda confusing honestly

go to the topic --> press the track button --> press the untrack topic button

On your tracker the right side has a date and hourglass. Click that and it gives the option.

You can click on the hourglass icon to untrack a single topic.
To untrack multiple topics, select them by clicking the number in the front row and then click on the edit pencil on the top to untrack them.

select the post count on the left side:





then select the tracking option at the top.

Ty