In the Writing Assistant palette I see a way to enter an Equal Symbol Aligned Math Cell, which would be useful both for input to be evaluated and also for formulas in the “DisplayFormula” cell-style. Is there a way to enter an Equal Symbol Aligned Math Cell without opening the palette or using the mouse?
You can insert the invisible \[AlignmentMarker] at the positions that you need to align, then add the option TextAlignment->AlignmentMarker as a cell option (after revealing the cell expression, or with the Option Inspector). Quite arcane.
If you need alignment in the output cells it is simpler:
Column[{a + b == c, c == a + b}, Alignment -> "\[Equal]"]