Yes, but only slightly — all VPNs slow your internet connection a bit because they require routing your traffic through an encrypted server before sending it to the destination site. Good VPNs will be able to minimize this slowdown to the point that it’s not noticeable.
Surfshark provides fast speeds when connected to nearby VPN servers. During our tests, my colleagues and I experienced an average slowdown of around 13% when connected to nearby servers. This is pretty good, although not as fast as some top competitors like ExpressVPN. That said, when connected to more distant servers, Surfshark slowed our connection by as much as 84%, which is considerably more than competitors. I recommend using ExpressVPN for a consistently fast VPN connection.