Most guitar TAB charts print a tempo marking around 100 BPM — folk, pop, and acoustic practice pieces all default there. 100 is the right universal speed for adult beginners.
This page is set to 100 BPM, 4/4, uniform click (every beat equal weight, no accents). For strumming patterns specifically, uniform beats are actually better than drum-style accents — you stop relying on the downbeat to find your place and instead focus on whether every single strum lands cleanly on the click.
Count "down-down-up-up-down-up" against each beat. The first three weeks will feel like a lot of work, but your timing will fundamentally change. After a month with a uniform click you cannot go back to playing without one.
The app pre-sets to 100 BPM, 4/4, uniform mode. To adjust, use the controls inside the app after it loads.