Typically I use OneNote to keep all my setting and adventure notes organized.

For managing the stable of NPCs, I use Google sheets to track the name, summary, faction, location, and disposition towards the party.

This campaign, I've been using notion but the previous campaign I used a google sites to make nesting webpages and keep campaign info on there. I made all the pcs authors so they could also update their characters, add information, etc and it worked out okay for a front facing solution. We never hit publish on the site so we didn't share it beyond our group, of course. As long as you have a way to keep yourself organized it's much easier to deal with the twists and turns that campaigns take.

I have used kanka.io for a while now and I'm satisfied with it. While I would prefer to self-host a solution or have an automatic offline backup and editor/viewer I cannot be that bothered. There are wikis that would allow me to do that but then I would have to set up and all that. Used a wiki before migrating to kanka.io and it was kind of a pain to set up, use and update.

While finding something better than my wiki I tested a few other services but found them coming with too much bloat. Mind you this was several years ago and they may be more modular now. That was what made me settle on kanka.io, its modularity. I also feel it is leaning more into worldbuilding than campaign management.

A bonus is that private pages are available in the free package so you can just share the whole campaign with your players and they can only see what you want them to see.

I've tried to adopt note taking tools mid campaign and let me warn you, it's nearly impossible to move all your content over. I had dozens of documents and the like on Google drive, several pages of rough notes on my desk and one player who's journal was so good I normalljust asked her.

That said, Sly Flourish's Notion document ticked all my boxes in a recent oneshot I did, my only issue being my lack of familiarity meaning I had to spend a moment finding the right space.

As opposed to bespoke campaign management like worldanvil, notion can be built from the ground up. Mike of Sly Flourish has already done the work but as we build familiarity with the tool, it will be easy to monkey with and end up with a perfect tool.

It'll take you a ridiculous amount of time to move all the content over, and let me just put an idea out there that you can decide if it's right for you.

If it's getting too complex for you to track, check in with your players to see if they can keep track themselves. If they can't, that's a prime point for your antagonist to thin the herd. In my regular game where I'm currently a player, the DM orchestrated the mass demise of two bloated and powerful factions, resulting in some amazing plot and much less for everyone to keep track of.

I've had a lot of success using Obsidian for managing and organising information (both for campaigns but also just in general).

You can link to other pages in your notes, there's a canvas feature if you like that sort of thing and my personal favourite, the graph, where you can see how all your pages connect to eachother.

It also has a lot of community plugins some of which are useful for campaign stuffs like Obsidian Leaflet(maps) and Fantasy Statblocks.

I use onenote for almost all my campaign notes. I've used world anvil as well. It's really slick but a bit more work to create and keep updated.

I wish 5e had a good adventure setup sheet. Something like Monster of the Week has for their mysteries would be really useful.

@KoboldOfArtifice wiki software my dude. i used to keep all my campaign notes in a project wiki on github. and have recently been using vimwiki. that way stuff can be hyperlinked instead of linear. and vimwiki has a good tagging system. and it's all plain text so you can search it really easily.