I can't claim to be an expert, and this is strictly in a USA context, but I'd explain it this way: "Liberal" is used to insult someone for having and promoting bad, insufficiently leftward political principles, instead of good ones. The good ones depend on what principles the person doing the insulting holds. The right side of the political spectrum also uses Liberal as an insult, so it can be confusing.

Elements of the far left consider Liberals hardly better than (and in practice indistinguishable from) political centrists, conservatives, or fascists, due to the perception that Liberals support policies that won't disrupt systems that perpetuate injustice, and will carry water for other liberals even when they commit acts they would denounce their political opponents for doing.

The right uses Liberal as a catch-all term for leftists generally (whom they despise), but it has diminished a bit, being supplanted by "woke" "groomers" "antifa" and "BLM."