From my experience of looking after two parents full-time for many, many years with dementia, the appalling help you get from the NHS, which is close to zero, means you need to turn to other sources for help.
The Alzheimer's Society and Dementia UK can be helpful, and I can't remember which one, but there is a helpline staffed by nurses who are lovely. However, I did find the advice can be very general and often doesn't fit what you are trying to work through.
YouTube and TikTok were my friends when it came to looking after my parents. Reading current research that hasn't reached mainstream treatment plans was helpful, but you have to dig deep. Also, listening to people's personal experiences and what worked for them or their family members helped me to develop a regime, particularly for my Dad.
It is all well and good to tell people to avoid these resources. I am crossing everything for you that your father has something that can be treated easily. However, if it is dementia, it is a long, lonely road, and if you are anything like me, you become desperate to try and help your loved ones in any way. I cannot tell you how many times, firstly, trying to get access to an expert is nigh on impossible, but when I finally did, they were rarely able to answer my questions.
I turned to supplements and diet out of desperation after extensive research and listening to people's stories. For example, the cognitive enhancer that a nutritionist advised my Dad to take. I would see a definite decline when he wasn't taking it because it was often out of stock, compared to when he did.
I stick by what I said, if he does have dementia, then the tablets can help. For example, my father took Memantine, and while it can have side effects (he never suffered any). They introduce it very slowly, increasing the dosage gradually. From just a simple Google search, you can see that Mayo Clinic writes about Memantine.
"Memantine may help slow the decline in memory and thinking skills. It also may play a role in protecting nerve cells. Memantine is approved to treat moderate to severe Alzheimer's disease. It's usually taken as a pill or liquid twice a day or as an extended-release pill once a day."
There are a lot of different tablets now compared to when my father was first diagnosed.
You have been given great advice about infections and problems with his ears. Those can be a contributing factor to a change in behaviour in ageing parents so ruling out anything else is the first step. Also, what I learned, the hard, way is symptoms and the way they react are very different and I had to get used to picking up on different signs particularly around behaviour.
I think you sound like a wonderful daughter, and I wish you all the best.