You say you tried to get him to be there purely for your daughter's sake, and think daughter would be wondering why he wasn't there.
This is what you tell yourself, but I think you are projecting your feelings onto her: it was for your sake, not hers, that you wanted him there. You missed him, she didn't. You were wondering where he was, she wasn't.
Here is the thing: 4 year olds don't notice, don't care, and certainly don't remember. From her point of view, she had so many other things to think about and notice: her uniform, her lunch, the other children, the teacher, the building, the playground, etc. etc. She absolutely did not miss him.
She knew you were there - that is all she needed.
I think you need some counselling to help you separate your feelings from your DC's feelings.
It is natural that the children will have moved on to the 'new normal' so much more quickly than you. They are adaptable, take things in their stride, and don't know any different. It is you that are struggling to get with the new normal (totally understandable, it has only been a few months).