Just trying to mitigate the Log4j2 vulnerability which affects Solr.
No way to update to the latest Solr version, because of the Sitecore dependency on the specific Solr version.

Well, particularly for Solr 8.1.1 I just decided to exchange all the log4j*2.11.jar's to the appropriate 2.17 ones within "server\lib\ext" folder.
Solr is still working after restart, and even writing log.
I hope that is the right way :)