Nowadays anyone bragging about their IQ should be considered a moron and left talking to themselves.
For example: https://www.youtube.com/watch?v=W3oUqKUx2o0 (first thing that came off my head)
That said, I agree if you brag about your IQ you're a moron.
imperfect measures are not always useless, which is goof since all measures have some error.
A test trying to measure something we can't even properly define is kinda flawed in it's whole premise.
As such the best an IQ test can do is measure how well somebody prepared for a test like that, but it will struggle to properly catch any knowledge or skill domains not covered by the test, of which there are a lot.
You can say "There is this test, and people's scores on this test correlate with various things like, income, marital fidelity, religiosity, incarceration rates, job performance". We call this test the IQ test.