I extended Barnys answer and ended up with this template.
Don't know why they do not call it a "bug" but a limitation https://issues.redhat.com/browse/KEYCLOAK-5034
for HTML
<#outputformat "plainText">
<#assign requiredActionsText><#if requiredActions??><#list requiredActions><#items as reqActionItem>${msg("requiredAction.${reqActionItem}")}<#sep>, </#sep></#items></#list></#if></#assign>
<#assign requiredActionsValues><#if requiredActions??><#list requiredActions><#items as reqActionItem>${reqActionItem}<#sep>, </#sep></#items></#list></#if></#assign>
</#outputformat>
<html>
<body>
<#if requiredActionsValues == "VERIFY_EMAIL">
${kcSanitize(msg("emailVerificationBodyHtml",link, linkExpiration, realmName, linkExpirationFormatter(linkExpiration)))?no_esc}
<#elseif requiredActionsValues == "UPDATE_PASSWORD">
${kcSanitize(msg("passwordResetBodyHtml",link, linkExpiration, realmName, linkExpirationFormatter(linkExpiration)))?no_esc}
<#else>
${kcSanitize(msg("executeActionsBodyHtml",link, linkExpiration, realmName, requiredActionsText, linkExpirationFormatter(linkExpiration)))?no_esc}
</#if>
</body>
</html>
for plain text
<#ftl output_format="plainText">
<#assign requiredActionsText><#if requiredActions??><#list requiredActions><#items as reqActionItem>${msg("requiredAction.${reqActionItem}")}<#sep>, </#sep></#items></#list><#else></#if></#assign>
<#assign requiredActionsValues><#if requiredActions??><#list requiredActions><#items as reqActionItem>${reqActionItem}<#sep>, </#sep></#items></#list></#if></#assign>
<#if requiredActionsValues == "VERIFY_EMAIL">
${msg("emailVerificationBody",link, linkExpiration, realmName, linkExpirationFormatter(linkExpiration))}
<#elseif requiredActionsValues == "UPDATE_PASSWORD">
${msg("passwordResetBody",link, linkExpiration, realmName, linkExpirationFormatter(linkExpiration))}
<#else>
${msg("executeActionsBody",link, linkExpiration, realmName, requiredActionsText, linkExpirationFormatter(linkExpiration))}
</#if>
don't forgot to put the template changes in all instances of the cluster and restart each cluster instance
sudo systemctl restart keycloak.service