The answers are:
Set Trigger to when a defender for Cloud recommendation is created or triggered

Trigger the execution of LA1 from Recommendations.

If you set the trigger of a logic app of a particular type, then you can only trigger it from that type.
For e.g. if the trigger is alert , then you can tigger the logic app from a alert & if the trigger is recommendation, then you can trigger it from a recommendation.

https://learn.microsoft.com/en-us/azure/defender-for-cloud/review-security-recommendations#explore-a-recommendation