Some devices can't use cards with a capacity of more than 32GB (as the technology for such cards is slightly different). So I strongly suggest not getting tempted to buy a 64GB card or greater, as it might not function properly. Just stick to the 32GB recommendation.
It's worth taking note of the 'speed class' of a microSD card but, unless you're buying an 'iffy' ultra-cheap card from eBay or similar, any modern card should be able to handle the data transfer speed required by your digital binoculars.
In your situation, I'd simply head down to Asda to buy one of these, which can easily meet your requirements:
https://groceries.asda.com/product/data-storage/kioxia-micro-sd-card-with-adapter-32-gb/1000223013573
(Note: That recommendation isn't simply the result of a bit of googling. I use those cards myself and I'm totally happy with them).