Footer Text Position is Not Effected by Changes in Offset or Alignment Settings
The default position of Footer text is at the lower margin position set at Format-Page Settings.
With previous versions of MuseScore, the Footer text position could be simply changed by changing the Vertical or Horizontal Offset position settings under Footer in Text Settings. The Offset values for Vertical & Horizontal were expressed in units or Staff Space.
With MuseScore 3.0.1, Footer text position is UNAFFECTED by ANY changes made to the Footer Text Styles X/Y Offset position settings which now has no option for Units and is only expressed as Spaces.
The same issue was noted when trying to reposition text using Copyright Text Styles.
The only change that has any effect on either Footer Text or Copyright Text are Font settings for font type & size.
Also, an Apply button to apply the changes is no longer present in Text Styles in MuseScore 3.0.1 so applying a change to see it is satisfactory is no longer possible. You must select OK and hope, or go back to Format-Styles-Text Styles-Footer if the change wasn't satisfactory.
No sample score was submitted because it happens with all existing or new scores created with MuseScore 18.104.22.16887