//relying on the built-in Windows Security software is perfectly good enough (and probably less likely to slow your machine than some third-party offerings).//
As I have been saying for at least since Edge was introduced and Defenders subsequent sand box anti virus improvements. 7 years or so? It takes a while to get through. Third party security extensions will want to turn off your built in security, bombard you with "offers" on upgrades, pass on your email details or at least retain them, use up pc resources and processing ability or speed, particularly on a laptop, and can cause problems with Microsoft upgrade progression. I have only ever, and still do, used Trusteer Endpoint which is an online payment additional check. It is advanced endpoint protection check designed to protect users from financial malware and phishing attacks, compatible with Defender and does not switch it off or compete. It is just a belt an braces thing for payment to sites that you have never used before if they are not well known brand sites. It is free and used to be compulsory if you wanted to bank on line.
The bit in brackets did make me laugh though. Remembering previous similar threads. You may have noticed that most of the threads that have slow laptop or load speeds all have one thing in common. Third party security. You need a very well specked laptop to handle it and need to be teched up yourself to control it.