The bias check is for the news. That is all. I also mentioned that in an above post. A bias check is not checking Songs of Praise or Eastenders. Just the news. And that is what matters here.
And all UK TV news has OFCOM rules on impartially to follow. Rules that Youtube channels etc don't need to follow.
Re the Good Law project reference part you mention. The bias check site is listing the major claims of bias. It is not saying if they are right or wrong. It is just listing claims made. It mentions claims that Trump made. That does not mean it supports Trump.
And there is this in the report, with links
"In past reporting, the BBC has been criticized by both the political right and left. Notable examples include the Evening Standard and The Times of London."
Again, they are not saying what is right or wrong. They are listing some of the claims made.
That is how it is supposed to work. They look at the claims of bias, throw all those claims in a pot, and see what the mix looks like. Then publish their bias score.
So when you say, quote "one of its sources was a very poor choice,", no, it's actually not. It's a bias check site. Do you really think they don't know if claimants might be biased or not ? It all goes in the pot.