How are you measuring your steps? Not to be harsh but it doesn't sound realistic. Out of interest I just looked and 8k in 80 minutes is roughly 5mph so you would have to be walking at 10mph to achieve that. You may well just be really speedy but if you think you are doing more than you are it can really skew things and make you disheartened. That’s really not me being passive aggressive so I hope it doesn’t come across that way, it’s just something that stood out to me
I don't have any personal knowledge of underactive thyroid or peri menopause however these possibly mean you don't burn calories as quickly? Hopefully someone more knowledgeable than me will be able to offer more info/advice
Good place to start would be to put what you are eating into my fitness pal or similar. It's really helpful to know what calories you are consuming to allow you to set a realistic goal. I was honestly shocked by the calories some things contain, and how low other things are. For two eggs, two bacon and 100g of avocado is about 500 calories. It would then depend what type of milk/cream cheese and how much you add. Even onion. It is tedious, and might sound extreme, but weighing food is really important if tracking calories. Also remember to include things you may use without thinking, oil, dressings, sauces like ketchup or mayo. You've mentioned no alcohol which is great as that really packs empty calories in. It is more expensive so won’t be possible for everyone but if you buy 12% fat mince maybe look to switch to a lower %. The difference between 12% and 3% fat beef mince is quite big per 100g calorie wise although I appreciate that flavour is in the fat, and calorie counting isn’t for everyone, but it has helped me have a better understanding of what I’m consuming. Your meals don’t sound bad at all but some slight tweaks could make all the difference. At the end of the day you just need to be in a deficit to lose weight. 3,500 cals if roughly 1lb, so that would be around 500 calories a day deficit to lose a lb a week
Again I’ve never personally tried slimfast or Huel, although I imagine it could take some of the headache out of calorie counting?
Sorry for the long post but I hope it was somewhat useful!