Not able to install "Search API Solr Log" submodule in versions 4.3.8 and newer

That is intended. I won't backport that to facets 2.

Understandable, but as this is a change that impacts everyone who is not using Facets 3, shouldn't that release have been a minor version bump instead of a patch? The way this has been done prevents everyone who is not using Facets 3 from getting security updates.
But thanks for the reply! We will keep using the version that supports Facets 2. Can you confirm that it is version 4.3.7?

search_api_solr_log never supported facets 2. The dependency to facets_exposed_filters was part of the initial commit:
https://git.drupalcode.org/project/search_api_solr/-/blame/4.x/modules/s...
So I don't know how you installed it without facets 3 before.

I totally agree that we should do more major or minor releases instead of patch level changes.
But we had that discussion multiple times in the past. Some Solr hosting providers and/or Drupal service providers don't understand semantic versioning correctly (I don't want to publish names here). They reject to apply important changes or bugfixes quickly if that requires a major or minor update which must run to additional "quality assurance processes".
In the past, that put a lot of additional load on the project to maintain multiple versions. We can't cover that in our free time.

So we had to react with keeping Search API and Search API Solr at the same major.minor for quite some time now to bypass their stupid rules.