Am I correct to say the US govt and municipal bonds and related ETFs, are generally exempt from WHT but not individual corporates?
No. Let's assume a non-U.S. person (without any effectively connected income from a U.S. trade or U.S. business) is holding these bonds/bond funds....
1. Individual U.S. government, municipal, and corporate bonds: not U.S. taxable.
2. U.S. bond (any type) funds domiciled outside the United States: not generally U.S. taxable at any level.
3. U.S. government and corporate bond funds domiciled inside the United States: might be subject to withholding tax (varies), but withheld tax can be recovered (later, without interest) through a nonresident tax filing with the IRS; U.S. estate taxable.
4. U.S. municipal bond funds domiciled inside the United States: generally no U.S. income tax; U.S. estate taxable.
I saw some bond funds with WHT at 80-90% range instead of 100%.
U.S. bonds are generally eligible for the portfolio interest exemption. There might be a few non-exempt bond-like instruments in existence.
Why all the interest in U.S. bonds, though?