• jszip uses a require("core-js/library/fn/set-immediate") statement at one point
• A Babel build with @babel/preset-env and "useBuiltIns": "entry" uses a custom-minified version of core-js including only the polyfills needed to make the list of that project's supported browsers work
• The resulting bundle doesn't include setImmediate (because nothing in the bundle actually references setImmediate as a global function)
• ...which leads to jszip breaking, because it's trying to require something not in the bundle
• ...which leads to exceljs breaking the first time it tries to use jszip

The "right" behavior here would be for jszip to stop trying to directly include polyfills (and leave that up to the end user like it should), but since that project is effectively unmaintained at this point, any practical bugfixes will have to come from other projects switching away from using it.