Some mailing lists at [1], like oss-security & kernel-hardening. CISA (Cybersecurity and Infrastructure Security Agency) [2] has a few different areas they report on. Mozilla has the dev-security-policy mailing list for all things PKI (public key infrastructure) [3], and a few other lists as well. There's the Full Disclosure [4] mailing list for vulnerabilities/exploits, etc. Quite a few others at [5], though sadly many are no longer active.
You have different areas of security. Sadly our space is full of grifters and wanna be security "experts". For a very technical security podcast I recommend Critical Thinking Bug Bounty [1].