Add Trend Lines to Line Chart

Hi dogt1225 
The trend line is a feature that is available only with a continuous X-axis.
The continuous x-axis can be only for numeric / date data type values.
On the attached image it is text....so you should use another format for the period like date or month year numeric like 112024..etc

There is an idea about the issue you can vote for it here :
https://ideas.fabric.microsoft.com/ideas/idea/?ideaid=2722c068-b9b5-ec11-bea1-501ac50a5d5c

As a workaround, you can use linear regression with the Dax method, please refer to the linked blog post of Daniil 

https://xxlbi.com/blog/simple-linear-regression-in-dax/

If this post helps, then please consider Accepting it as the solution to help the other members find it more quickly