Is investments in vanguard accounts safe?

No

How can investment be insured? Only money in bank can be insured

Yes, if vanguard went under you would still own the underlying assets. They are just a broker

Yes, it is covered by the spic. As the other poster said, a brokerage account is not a bank account. They don’t lend out the deposits. You own the securities you buy, so it’s not like they can just disappear if the brokerage goes under.

Security is a myth, my friend

Nope.

SIPC insures you in case your broker goes bankrupt. When you buy Vanguard securities, Vanguard is the issuer. You won’t be insured in case your investments lose value.