I can empathise completely with this. I have never felt a bond with either of my adoptive parents. My Father was an academic, aloof and emotionally cold and had very little time for us. He was unquestionably an undiagnosed autistic. My Mother is a bitter and twisted person and a bundle of neurosis. They are both 90 and during Covid my Dad was diagnosed with Alzheimer's disease. The cruel thing about Alzheimer's is not simply that it robs your memories, but your very identity, the person you were. Strangely, it has transformed him a very gentle, warm and appreciative person. All the cold harshness and regimentation is gone. Ironic that the very thing that defined him and his career, his brain, is now deserting him, which is very hard to witness. My biological Mother is Welsh and her husband has vascular dementia which is equally as cruel. My real Dad is an Irish rogue - as much as he irks me, I really should track him down again. Life is so short. I fully understand your sense of their imminent mortality and as you say, the demise is hard to process.
Upshot is, I'm not a family oriented person. I am very close to and adore my daughter and son-in-law, whilst aside from them, from day to day the only real love I feel is for my partner...and our dog. That sounds quite tragic, but I really try to avoid emotional investment. It's harrowing enough supporting City.
I wish you well over the Christmas period and for the New Year my friend.