Custom workout question on Fenix 5 plus


I've got a Fenix 5 plus and am trying to start getting fit (am starting out from zero after years of little/no exercise due to knee injuries).  Three weeks ago I began using the "Run" activity 3 times a week to do an easy 2km jog, just to try and get started.  What I'd like to do is add some activities (sit-ups, squats, push-ups) into an intervals workout, eg 500m jog, a set of each of the moves, then 500m more, then another set, then 500m more and so on. 

I've tried creating a custom workout in Garmin Connect but it doesn't seem possible to mix "types" that correct?  I can see the workout types "Run" and "Pilates" (which contains the push-up/sit-up moves) but when I try to add one to the other as additional step, I don't see any option to do so (Garmin Connect Web).  When I try to create a custom workout, I don't see any of the moves?

Am I missing something?