My experience was it isn't particularly easier or harder than any other language to learn.
The grammar and word ordering is different enough that you really have to study and practice a lot how to structure sentences. Pronunciation of some sounds (like 'ui') can be pretty hard if you've never had to make those sounds before in your life.
But indeed the spelling is much more consistent than English, which definitely helps a ton with reading and writing.
I moved to the NL 14 years ago, took the Staatsexamen for naturalisation after Brexit, have had a couple of jobs where Dutch was the first language, but my Dutch still isn't perfect and I regularly make mistakes.
That being said, I am now finally at the stage where I can go on a day trip to Amsterdam and the locals don't speak English back to me when I speak Dutch. :)