Custom Case Deflection in Lightning Community [aura]

You can use the case deflection component on its own, just need to tweak your form to register the event used by the deflection component and fire it with the field + field value parameters on field change or blur.

For example:

Note:

• The OTB community Case Deflection component will update automatically.
• Event only available for Aura components for now. Not available for lighting web components

Sources :
https://salesforce.stackexchange.com/questions/214342/case-deflection-component
https://developer.salesforce.com/docs/component-library/bundle/lightningcommunity:deflectionSignal/documentation
https://developer.salesforce.com/docs/atlas.en-us.communities_dev.meta/communities_dev/communities_dev_case_create_deflection.htm