Mum really dragging me down.

It can be pretty joyless getting old!
Contact Age UK perhaps? They might have some advice. Some places you can access befriending type services where someone could ring your Mum for a chat.
When you see your Mum, what do you do? Sit and chat? If so, perhaps try and change that to doing something? Like a jigsaw or take some bulbs to plant in a pot? Being more occupied might distract her a bit.
My DH visits his elderly mum in her care home. She's often quite grumpy and he finds it hugely draining. He usually takes something within, like a few old photos which often works to get her thinking about something else.

Do you have to visit as often?

Is this where the right carer support can lift some of the burden?

I'll bet that it's part of the development of her illness. Think of is as if her brain has gotten a fixed thought pattern like an old fashioned record on a loop. Nothing you say or do will change the way her brain is processing her experiences.

Accepting that is hard.
Really hard.
But if you accept that its a pattern you can't break or change the outcome it should be easier for you to manage your emotional response.

Changing the subject, just agreeing with comments, ignoring conversational openings, distraction by talking about something she likes etc.
There are numerous options which you can use to participate in her conversations but dont try to solve "the problem" you mum comes up with.
Stock phrases "Hummm", "Yes Dear" "Right" etc shows you heard the sounds but are not really giving your own opinion. Its finding what works for you (complaints bingo whatever)

Has your mother been referred in for specialist geriatric care? There are some meds which can help slow memory loss and she may be depressed on top of everything else.

You may already have the link below
www.nhs.uk/conditions/dementia/help-and-support/#:~:text=Alzheimer's%20Society%20runs%20the%20Dementia,life%20for%20people%20with%20dementia

You should also see it there are any local carers groups who talk with you and offer moral support.

If you did take her out every day would she even remember?

I suspect she is moaning not because grandchildren don't go round/she isn't part of the family etc but because she can't actually remember what does happen and she gets bored during the day.

A big part of dementia is not being able to initiate activities - you give examples of this such as won't go to day centre, wears scruffy clothes, wouldn't join classes. But then having not initiated anything doesn't mean the person with dementia isn't flailing about desperate for some distraction and actually really bored.

Social services assessment is a good idea, with either day centre or carers being presented as not optional - once they are there, it's very likely she'll like them as her time will be filled and she will have the social connection and activity she needs.

You are not responsible for her happiness. Try to erect an emotional barrier, treat her as if you were her social worker. Cheery sympathy without any promises to put it right.

. Remind yourself that her complaints aren’t aimed at you, they’re just her frustration that her life is no longer what it was. Do whatever you need to to let them roll over you - complaints bingo, count how many whinges in the first 15mins. Anything that turns her from a person with emotional hold over you to a lab rat to be observed.

And if that sounds harsh, remember lab rats by law are treated well.

My mum has always been like this and it is exhausting. I have distanced myself as much as i feel is possible but this gets harder as they age and become more in need of support. When they refuse outside help it can really make you feel trapped. Sorry i cant provide a solution but l hugely empathise.

Stop going every day or cut the length of each visit?

Having carers to support with shopping, meal preparation etc can break the long periods of being alone.

Are there any day centres that she could go to locally?

It’s tough op.