you can manually click on their profile and then click the three dots at the top and block them so they can't see you anymore but I'm not sure that takes them off of your follower list. And doing that a few thousand times would take forever. A lot of those followers are automated. People set up a program to automatically follow thousands of people hoping that you will look at their profile and follow them back. Sometimes they follow and unfollow you over and over again which is really annoying.
Yes it is I just spent 30 minutes unfollowing over 300.00 it was easier doing it on the computer and not my phone.
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