Never knew I needed? Another vote for Paperless-ngx. I still feel like I'm living in the future using it. The trick I've found was initially setting up a good document naming & management convention & following it religiously for every document. The search function is fantastic at narrowing down results. Used in conjunction with specific coloured tags I can immediately see what I need from search results.
Fired up Immich recently. Amazing. Will be donating as I like their stance.
I also enjoy Linkwarden. Switched from the also excellent Hoarder as I prefer the UI.
Most used? Nextcloud with Joplin.