How can I delete many of my activities at the same time? I can't delete 146 activities one by one...

1011348 said:

I have a fenix 6x. I have many many activities, but I would like to delete most of them. How can I do that?

If you mean deleting them from the watch, then the easiest is connecting the watch over the USB cable to a computer, and deleting the files in the folder //GARMIN/Activity/ 

By deleting those, the activities remain preserved in your Garmin Connect account. If you need to delete them from there too, then you can do it more comfortably on the List of All Activities in Garmin Connect Web - see the icon of a bin on the right end of each activity row, when you highlight it.

Well, I did not really mean highlight as the selection - that's for comparing the selected activities. Rather just moving the mouse over the row, and the bin icon appears on the right. You can then quickly delete the activity. In this way deleting multiple activities is rather fast. So unless you need to delete hundreds of them, it should help. If you really have to delete a huge number of activities, then I am afraid you'd need to run a JavaScript command through the Console. I believe the user BunBun! already posted such a snippet here in the past, so it should be in the forum archive. Unfortunately I did not bookmark it, but perhaps BunBun peeks in.

This thread might perhaps help or give you some idea:

https://forums.garmin.com/apps-software/mobile-apps-web/f/garmin-connect-web/165851/can-i-delete-just-the-activities-from-a-single-garmin-device-from-my-garmin-connect-account 

Yes, there is a script to remove activities in this thread: Loaded rides by mistake - with linked script to search activities by device. IF can be changed and you can add filters to the first link, copy them from the Advanced Search on the activities' page.