Is it not? The US doesn't require minimum turnout for elections, so not voting just amplifies the power of the people who actually vote. It is in effect a tacit endorsement, unless you're trying to effect legal or regime change in addition to not voting.
As far as "my vote doesn't matter", this is quite silly considering how the last two elections featured electoral votes won by ever thinner margins, and that even at the presidential level with the highest turnout most people don't vote, to say nothing of state local elections, primaries, etc. https://i.redd.it/p0z5srsw7py51.png
