I haven’t played a strictly solo character, but I felt so disconnected from my group I ended up joining another. I get very little fun out of groups which aren’t into the same things as me, and end up being a functionally solo character chasing stuff I like. I ended up finding a perfect match group in the end though, but I found it myself IC.
I think it’s entirely possible to work as a solo character in the sense of not being connected to a group in a nation as long as you engage with cross-nation structures, for example Conclave orders or the Synod.