Well you've asked for advice but you don't like it because everyone agrees with you that you've been selfish & inconsiderate. Grief hitting you hard this year might be your reason for not showing a moment's thought to the person you supposedly love but it's not an excuse.
she wasn’t and shouldn’t be fine with this but why do I feel not seen ? Why do I feel like my struggle over this time of the year has gone ignored and taken a back seat because of the lack of a present
Because it isn't just a "lack of present". It is, in your own words, selfishness. You have said yourself that you've given no thought whatsoever to Christmas, or to her. She is, presumably, justifiably deeply hurt by this and, what, questioning your reformed relationship?
Completely ignoring her existence at Christmas, which is effectively what you've done, while take-take-taking everything, because you've been hit by a wave of grief is not the behaviour of a committed partner. It's the behaviour of a selfish individual who cares only for themselves. Calling out everyone who tells you you're in the wrong and suggesting they're being sanctimonious doesn't change this.
It seems to me what you're looking for is for people, perhaps men if let down by women here, to tell you that you what you did what shit but understandable and she should cut you some slack. What is your plan if no one will do this?
Will you reflect on your behaviour and perhaps consider that your grief & overwork is no excuse? Or will you just assume that everyone on mumsnet is too perfect and does not understand your grief?
I am sorry for your grief over the loss of your mum and grief does have a habit of hitting us hard when we don't expect it, but it doesn't give us a licence to treat others badly.
The best advice I can give you is to be accountable for your shitty behaviour, apologise and in the new year find a bereavement counsellor to help you through this difficult time, while making an effort to be a halfway decent partner. That is how you will find your struggles are seen and acknowledged.