I encountered the same issue after upgrading Solr from 9.7 to 9.8: Error loading class 'solr.extraction.ExtractingRequestHandler' .

The solution in 9.8+ is to activate the module with an environment variable (see docs):

SOLR_MODULES=extraction

While in 9.7 and prior this was done in the solrconfig.xml, as stated in the older answers here (9.7 docs):

  <lib dir="${solr.install.dir:../../..}/modules/extraction/lib" regex=".*\.jar" />

Hope this helps people who face the same problem.