I used Excel sheets with a small grid scale & cell merges to build page layout prototypes for a startup. Didn't have to climb the Figma learning curve (no disrespect to Figma, I'm sure it's great). Would do it again.
Just for drawing mock app screens, I have found Balsamiq[0] to be pretty good (you can do a bunch of stuff with the trial version itself). Not affiliated with them in any way.
[0]: https://balsamiq.com/