You could try this link. Homeyscript deleting timeline.
I didn’t check if it works correct after i bought the new Homey pro, but the script and flows from my homey early 2019 were converted to the new Homey. I have to check the script when i am home again from vacation. But as far i know the script has one flaw(only on the new homey pro), it will not give a notification on your timeline when the timeline notifications are deleted.
But untill today i do not have a lot of notifications on my timeline and now and then the timeline is cleared, so i suppose it still works.
