Hi @Marty3012,
Please refer to screenshot below to get the date of the following Monday:

The expression in the Compose as below:
if(equals(dayOfWeek(utcNow()),1),addDays(utcNow(),7),if(equals(dayOfWeek(utcNow()),2),addDays(utcNow(),6),if(equals(dayOfWeek(utcNow()),3),addDays(utcNow(),5),if(equals(dayOfWeek(utcNow()),4),addDays(utcNow(),4),if(equals(dayOfWeek(utcNow()),5),addDays(utcNow(),3),if(equals(dayOfWeek(utcNow()),6),addDays(utcNow(),2),if(equals(dayOfWeek(utcNow()),0),addDays(utcNow(),1),null)))))))
The expression in the Compose 2 as below:
formatDateTime(outputs('Compose'),'yyyy-MM-dd')
The flow would run successfully as below:

Please let me know if your problem could be solved.
Best regards,
Alice