All Twitter users can now remove a follower without having to block them. The company started testing this option last month, and starting today, everyone will have access to it. To quietly stop someone from seeing your tweets in their feed, go to the Followers tab on your profile, click the three-dot menu next to the user in question and select the "Remove this follower" option.
rolling out to everyone on the web today👇 https://t.co/Nqhhf2q2fo
— Twitter Safety (@TwitterSafety) October 11, 2021
This is part of Twitter's efforts to reduce harassment on the platform. Blocking someone you don't want to follow you could lead to retaliation from that person via their allies or their secondary accounts after they find out. Cutting them in this fashion and muting them will mean they're none the wiser that they're out of the loop.
This method won't prevent someone you boot from your followers list from seeing your public tweets. Only blocking them or making your account private will do that. Elsewhere, Twitter is testing a Safety Mode, which automatically blocks accounts that use “potentially harmful language.” It's also looking into more ways to filter and limit replies, so it seems the company is making its anti-harassment efforts a bigger priority.