Repeat each row N times in Google Sheets

Without splitting and joining and other string manipulations,

=ARRAYFORMULA(FLATTEN(IF(SEQUENCE(ROWS(A2:A4),5),A2:A4)))

• A2:A4 The range to repeat
• 5 Number of times to repeat
• SEQUENCE to create a 2D array of numbers
• IF to transpose a 1D array A2:A4 to a 2D array of size equal to the SEQUENCE array created
• FLATTEN the 2D to 1D array.