I went through the tutorial documented at https://apache.github.io/solr-operator/docs/local_tutorial and the solr instances would not start. I saw that there was an error parsing solr.xml on the field "allowPaths" so decided to try version 8.7 since it looks like this was introduced in 8.6: https://solr.apache.org/guide/8_6/format-of-solr-xml.html.
When using 8.7 it worked! The tutorial explains how to do an upgrade as well, so perhaps it should start with 8.6 and then upgrade to 8.7? I did not try out 8.6, but perhaps someone could validate that if they agree with my findings. Anyway, just wanted to share this. Thanks!