As I said previously all your issues are related to the inferior Exynos variant. It isn't going to get any better.
Since importing the Snapdragon the GSM issues are gone, display is vibrant and REALLY bright and the battery life is very very good.
You're probably too late now to get any money back, luckily I sent my one back within the 30 days as I coud see it was plainly inferior to my previous Note 8. Even the Note 10+ Exynos is a far better handset.
Good luck. I notice Vodafone UK have completely removed the N20U from sale. I really wonder why?
Previous Note models were sold even when the new version came out.
I bet it's the number of customer returns.
As a guide, my N20U Snapdragon uses average 35% a day per the battery stats and that's brilliant.