To get rid of this warining, you have to add the following entries to your Wildfly standalone.xml:
Add the org.wildfly.extension.clustering.web extension inside the <extensions> tag
<extension module="org.wildfly.extension.clustering.web"/>
Add the <distributable-web> subsystem inside the <profile> tag
Wildfly 21:
<subsystem xmlns="urn:jboss:domain:distributable-web:2.0" default-session-management="default" default-single-sign-on-management="default">
<infinispan-session-management name="default" cache-container="web" granularity="SESSION">
<primary-owner-affinity/>
</infinispan-session-management>
<infinispan-single-sign-on-management name="default" cache-container="web" cache="sso"/>
<infinispan-routing cache-container="web" cache="routing"/>
</subsystem>
Wildfly 23 and 26:
<subsystem xmlns="urn:jboss:domain:distributable-web:2.0" default-session-management="default" default-single-sign-on-management="default">
<infinispan-session-management name="default" cache-container="web" granularity="SESSION">
<local-affinity/>
</infinispan-session-management>
<infinispan-single-sign-on-management name="default" cache-container="web" cache="sso"/>
<local-routing/>
</subsystem>