I’d screenshot, crop, and put them at a dedicated folder that will be synced uploaded to nextcloud via their app.

I print hard copies because (a) I’m a dinosaur (b) it’s easier than fumbling with a phone

I put them in my password safe

Like most others I use paperless-ngx.

On top of that, I use syncthing to sync the paperless files to my mobile phone. You can set storage path for each file in paperless; I have one for important files like tickets. Then I have them even without internet access 🙂👍

I also use email and company apps (flights, …) … 🫣 For movies I also use “note to self” in signal to quickly store and find them…