I haven't read the entire thread - deliberately this time because I just wanted to give an uninfluenced answer to your initial question.
I am a mid 40s woman who is definitely comfortable going into pubs on her own. I don't actually drink alcohol any more but still enjoy being in pubs sometimes, just to feel the world going on around me and for a bit of atmosphere. I have always done this.
I usually take a book, or might be on my phone, but I am definitely open to being approached by men or women for a chat. In fact just the other weekend I was out in a pub garden taking a break from shopping, enjoying the sunshine, and a fella who was out with his sons, who was about my age, spoke to me for about 20 minutes (we were both vaping outside). He told me a bit about his job history, which I found interesting. It was nice.
I am not single so not looking for a relationship, but when I have been single, I've definitely been open to meeting someone like this. I have had a few short relationships that started like this, and one marriage!
Just be careful to read cues, don't make a nuisance of yourself. Most people are good at making it clear when they don't want to chat - if she isn't asking any questions and her answers are very brief, politely move on.
And I'd suggest not getting to bladdered. Drunk people are boring and repetitive! (I can say this - i used to be one quite frequently!) A drink or two to relax you is fine of course.
Good luck - hope you find someone nice!