This is actually not true of the entire US! It depends on the state. When I worked in Ohio, we would encounter people who incorrectly believed they couldn't vote because of past felonies.
16 states allow people with felony convictions to vote once their sentence is complete.
9 states have restrictions on voting rights for people with felon convictions. Some of these are effectively a ban. One of these states is Florida, which passed a referendum to restore voting rights to people with felony convictions who had completed their sentence, but the DeSantis administration has found various loopholes to continue restricting voting.
23 states ban prisoners from voting but allow people with felony convictions to vote if they are not in prison.
2 states, Maine and Vermont, allow everyone to vote.
OP, I know you're not American and may or may not be interested in this, but it's important for any Americans seeing this to know that depending on where they live they may in fact have the right to vote. Misinformation about this is a form of voter suppression.