I haven't heard of them until like 2-3 years ago and I see them posted in World News quite often. What kind of a news source is this? Are they biased in some way? Where are they based? Is there anything notable to know about them?
They're the largest media org in the middle east and have been for decades. They're very good on some topics, and will reliably provide a different perspective from that of western media, but they are owned by the Qatari state, so you should be highly critical of stories that involve Qatar's interests, just as you would be of a BBC story involving British interests.
They are not consistently anti-imperialist, and on certain topics they are closer in their geopolitical stance to BBC and CNN than they are to RT or CGTN. The main positive thing they have going for them is that they are pro-Palestine (as it would be completely untenable for a news outlet of an Arab country to be pro-Zionist).
But you will frequently see them parroting imperialist propaganda narratives about China for instance. And that is no surprise since Qatar is a Western protectorate.
If you want actually anti-imperialist outlets from the Middle East you should try Al Mayadeen or PressTV.
Al-Jazeera is a media network owned by Qatar. It provides international voverage of news but naturally focuses on the Middle East region. Its political inclinations may vary depending on the country they're broadcasting to.
But generally speaking, it is pro palestine and anti imperialist. Evidently, its narratives may change with Qatar's geopolitics. For example, Al-Jazeera directed in the past a lot of criticism to Saudi Arabia, namely the war in Yemen and the murder of a certain journalist.
Ultimately, every media outlet has certain biases which is how journalism is meant to actually be. I can partly attest to Al-Jazeera's high quality journalism.