If you're a designer/developer and used the Edge F12 developer tools the new Edge Chromium was a major downgrade in this regard. So you may want to reinstall Edge just for this purpose.
If you have already installed Edge Chromium or it was installed in a recent update you can follow these steps to bring back the classic Edge and/or run both browsers at the same time.
First, download the Edge Chromium installer and Policy Files from here:
Now extract the Policy files any copy msedge.admx and msedgeupdate.admx from the extracted folder.
copy these to the C:\Windows\PolicyDefinitions folder on your computer.
Once you have done that then open group policy editor,
once open, under Computer Configuration go to Administrative Templates, Microsoft Edge Update, Applications then open "Allow Microsoft Edge Side by Side browser experience" and set to enabled.
now uninstall Edge Chromium.
Once its uninstalled open search and type "Edge" and the old edge icon should show up, pin this to your task bar because you will not be able to after Chromium is reinstalled.
Now if you want Chromium installed as well, install the .msi package from the step above that you downloaded from Microsoft downloads.
Now you should be able to run both browsers together.