It can be hard to overcome a lifetime of conditioning to be honest, especially to parents and elders.
I know we all feel guilt but it's not helpful. Here on Talking Point we often call it "the guilt monster" (GM for short) and remind each other to resist it. We even have a special (virtual) stick for bashing the guilt monster with, or if you prefer, a pointy stick with which to poke it.
Kidding aside, guilt doesn't get us anywhere. I have been reading about it and a few points stuck with me.
One is that what we carers call guilt may be other emotions, especially grief, but also anger, sadness, frustration, fear, anxiety, and so on. There can be a lot of ambiguous grief or anticipatory grief when dealing with some illnesses like dementia.
Another idea is to reframe your thoughts and statements, substituting "regret" for guilt. I regret my mother has dementia. I regret she had to move into a care home. I regret not spending more time with her. Or, I regret my parent has this rotten brain disease that means I have to lie to keep her comfortable. And so on; you get the idea.
Best wishes.