You can’t install /e/Browser but as irrlicht said it is a fork of Chromium, built from Bromite patch-sets, with specific /e/OS settings.
You can have some more information about browser in general here:
However you can install BlissLauncher (the /e/ launcher) on a “legacy Google phone” from Fdroid, but I think this is not the lastest version of BlissLauncher
A long time ago I installed the /e/ browser on other ROMs (Nougat/Oreo days). Version 79 was still on one of them. So yes, it can be installed (or at least it could). How well it runs is another matter.
On a side note: Also back then I had a couple of icon pack devs make an icon for it.
After a really long procrastination period I finally got around to installing the other default apps onto a ROM that has Play Store so I could do icon requests. They all installed except for Calendar (the only one that /e/ has under /product/ instead of /system/).
Did not try to actually run any of them, just needed them installed. Accidently launched Notes once and it crashed.