This year's save menu is kinda weird (as always tbh
)
Make your fav formation, then go to Data Management. You first need to copy your formation to one of those numbered slots.
The first one below "Now in Use" is your current formation, click it then click in one of the numbered slots right below "Saved Data" to save it.
Go back to Data Management and choose Save Stock Data.
To load it when you play again just choose Data Management/Load Stock Data then click on your saved formation which will appear in the numbered slots.. then click again in the first one below "Now in Use" to copy it.
OMG.