I’m trying out Trilium Notes for the last few days and gotta say it’s the closest thing to Notion I’ve seen, but it’s also Free software, which is amazing. The learning curve is somewhat off-putting and that keeps it from being a real and exciting alternative, but if I manage to get used I’ll probably stay.
I've been struggling with the same. I like Notion but I don't think the mobile experience works as well as it does on desktop. Trilium is the easiest to setup but I the UX makes it harder to work with than Notion for me. Overall Obsidian is closer to what I need but I don't want to fully move to it until I setup my own sync server that doesn't rely on their servers.