Whatever task management system you use, never ever write down a "task" that cannot realistically be done in a single sitting of work. If you can't do it in an afternoon at worst, it's not a task, and needs broken down further.
Set a ceiling for the number of items in your backlog. When I was using Trello/Kanban to manage my tasks, I had a hard ceiling of ten things in the backlog. If something isn't important enough to rate being on that top ten list, it shouldn't even be formally acknowledged until you have space to acknowledge it in. (And if something sits in the backlog for a while unaddressed while new things come and go, admit it's not that important and drop it.) This doesn't need to be "ten items". Whatever number works for you, as long as it keeps you comfortable. This is about managing anxiety, not managing work. A backlog too large to even count is overwhelming. Don't let that happen.
Write everything down, preferably on paper. The physical act of writing does wonders for memory.
I've recently converted from Trello to bullet journaling for managing my life, and it works a lot better, for me at least. Paper writing, plus the loose-yet-structured nature of the bullet journal, is really powerful for keeping thoughts in order.