the FSDG workgroup does not make formal statements or
proclamations, just evaluations and recommendations, for how to
meet the general FSDG criteria - this is all done on the
workgroup's mailing list:

https://lists.nongnu.org/mailman/listinfo/gnu-linux-libre

relatively few softwares have specific recommendations; but
chromium is one of them - one of the criteria for endorsement is:

from: https://libreplanet.org/wiki/Template:FSDG_Checklist

Programs commonly known to have freedom issues are liberated or

excluded

that is referring to the "ugly-list", where the recommendation
for chromium is "use icecat":

https://libreplanet.org/wiki/List_of_software_that_does_not_respect_the_Free_System_Distribution_Guidelines#chromium-browser

regarding electron/webengine, the short answer is "yes, there
are alternatives"; but they are not compatible with each other -
replacing them would require cooperation and and significant
effort from the authors of software using these libraries - the
better answer though, is that no one should want an alternative
replacement for these; because they have no value for the user
(in fact, the value is negative, in terms of CPU/RAM usage) - if
there is any value at all, it is a matter of convenience for the
developer

all they do, is to make a webpage appear to be, or be embedded
into, a desktop application - it is frivolous and tacky from an
engineering perspective; because a superior method of
accomplishing the task is always available and obviously so

the only reason you are asking that question is because
developers are (mis-)using them - that is the entirety of the
problem IMHO - presumably, it is not that you really desire an
alternative implementation, but that you want to be rid of the
existing one - there is a better way to accomplish that

the only satisfying alternative, is to convince those software
authors to stop using it, or at the very least, to allow people
to disable the requirement at compile-time, so as to use the
software without that feature - in almost every case, that
feature is non-essential to the program anyways - in every
use-case, the feature could be simply a normal web page, which
users would be able to access with their preferred client; or its
functionality could be implemented as a real native application