The other answers wrt security are correct but in ways that are even more serious than you might think. For instance, one could say "the OS is out of date, but my web browser is fully up-to-date, so therefore I am safe." This thinking is incorrect.

The web browser being up to date is of course, without question, necessary for security, but it still depends on OS libraries. If there is a bug in a feature that the browser relies on, e.g. memory allocator, then there is nothing you can do to protect your system against such an exploit. The allocator will never be fixed since the OS is unsupported. Newer OSes also tend to introduce features that software can use to improve their own security.

Consider this occasion where Chrome had a vulnerability that was only seen to be exploited against Windows 7 32-bit (in 2019, so Win7 was still supported by Microsoft at the time!) https://security.googleblog.com/2019/03/disclosing-vulnerabilities-to-protect.html