@damenora , you are correct in that you as a permanent resident ( GreenCard), and being in the USA ( Tax home USA), cannot seek US-UK treaty benefits. Thus you need to re-do your return for US. You can indeed seek to ameliorate double taxation by taking foreign Tax credit ( as long as there is foreign income ) --- use the form 1116 with lump sum distribution for the pension benefit. The life insurance, though , is another matter . If this was paid for by you then generally it should not be taxable or based on exact facts and circumstances you could be taxed only on the gain i.e. total received LESS total paid in.
If this is a 2022 return, then I would suggest not to rush but do it correctly , even if you are day or two late. TurboTax e-file would be open for at least another week or two ( I think ) because of rejected returns have three days to correct and re-file.
Good Luck.
If you need more on this , please feel welcome to send me PM or add to this thread.
pk
