i think on older computers they're necessary, but not as much on newer operating systems.
OSes like Windows 11, modern GNU/Linux, and MacOS generally don't need an antivirus, especially Linux since there aren't many viruses designed for Linux anyways.
Windows Defender in W11 is really good but it's not perfect, but i think you're mostly fine with that and being cautious.
though with older OSes (like older Linux kernels, Windows 8.1/8 and earlier, older MacOS, etc) are definitely in need of an antivirus of some sort. especially ones like Windows XP (which never had an in-built antivirus to begin with) but i'm just really wondering if it's even worth it since XP hasn't had any security patches since 11 years ago now.
can someone fill me in on that? :P
anyways also, my mum had Trend Micro (historically had Avast, and had i think McAfee or something last) and she got rid of all them. especially McAfee, she couldn't unsubscribe from it, so she had to get a whole new credit card. so i think some modern antiviruses are probably best not to get them.
idk it's just my opinion on it :P