Shift + { doesn't shrink

Yes.
However, you can go to Format -> Page Settings... and change the 'Staff space' to 1.620mm to fit 4 measures.
Another way: If you delete the instrument names, you won't have to scale down as much and can use a number like 1.700mm to fit 4 measures.
See:
https://musescore.org/en/handbook/3/page-settings#scaling

Also, you can tighten spacing within measures, see:
https://musescore.org/en/handbook/3/measure#options

Hello
If you have lyrics or chords at the top. then some may be too high and you'll need to grab and lower. Or go into F8 and make them smaller to shrink the staff. Also Format,, Style, page, disable vertical justification of staves - click on it to be black dot. the Max. system distance can shorted the staff. i often use this to get all on one page. Depends if you have one staff or grand staff.