This is not necessarily true. Speaking from experience as a DUI felon (no other charges) I have traveled to multiple countries in the EU, UK, Thailand, Costa Rica, Mexico and Dominican Republic. The only country that has denied me entry is Canada.
This likely depends on the felony of course. A DUI in which no harm/damage occurred is probably the lesser of the felonies.
You end up on a no fly list or become a convicted felon and that’s it, your life of travel is snuffed out.
I really feel for the OP.