I'd give Demons Souls a miss if you've not played many of the Souls games. It's a wonderful remaster but it's by far the worst game in the series, albeit much easier and a gentler introduction.
Elden Ring is a wonder of a game and would always recommend it. Thing is, you know what you like in games more than anyone. The challenge is what hooks me into these things, but if you're likely to be frustrated at the difficulty then I wouldn't bother.
Take a punt though, you never know...