How do I delete xpcproxy executable from /usr/libexec folder on my Mac?
You don't say why you want to delete it, so I'll assume you know what you're doing.
/usr/libexec is a folder for programs that are used by other programs. xpcproxy is owned by root, and so you'll need at least root privileges (typically via sudo) to delete it.
In addition, you may have Apple's System Integrity Protection if your OS is fairly recent vintage. If you have SIP, you'll need to disable it before you can delete this file. THere are numerous guides (like this one for Catalina) explaining how to disable SIP, so I won't repeat them here.