Do I need antivirus?

Reviewed answer

Not extra. Windows, Mac, and Android have protection built in, and iPhone doesn't need any.

On Windows, Microsoft Defender is built in and on by default. Search Settings for "Windows Security" to check it shows green.
On Android, keep Google Play Protect on and install apps only from the Play Store.
On Mac and iPhone, keeping the system updated is the protection. Apple's checks run in the background.
Skip "cleaner" and "booster" apps. They rarely help and some are the problem.

Get help if

If a pop-up says you're infected and gives a phone number to call, it's a scam. Real security warnings never ask you to call anyone.