Everything big in Admin Panel

1. Refresh the page in your browser.
2. Clear browser cache when logged out of site. Log back in.
3. Check the saved zoom level in the browser for this page. On Windows, hold CTL and 0 at same time to get back to default of 100% zoom. On Mac, CMD + 0.

Note to zoom, replace zero in above with + or -.

Are you in the Post/Page Editor or just at /wp-admin/ (Dashboard)?

Does Zoom work at all in Dashboard (as noted above?)

What browser are you using? Can you check the Dev Tools for it and see if you are forcing the site to be viewed in mobile view?