Dave wishes that Excel would offer a REPTARRAY function, just like REPT but for arrays. This video shows four different ways to repeat an array N times.

Vote for Microsoft to add REPTARRAY:
https://feedbackportal.microsoft.com/feedback/idea/0f6d6e22-7cb3-ed11-a81b-002248519701

Details about FastExcel: http://mrx.cl/speedv4

Here are the formulas used in the video:
=TEXTSPLIT(REPT(TEXTJOIN(“,”,TRUE,A)&”,”,$E$1),,”,”,TRUE)
=DROP(REDUCE(“”,SEQUENCE($E$1),LAMBDA(a,b,VSTACK(a,D))),1)
=LET(a,E,rw,COUNTA(a),MAKEARRAY(rw*$E$1,1,LAMBDA(r,c,CHOOSEROWS(a,MOD(r-1,rw)+1))))
If you have FastExcel V4 from Charles Williams: =REPEAT(A2#,E1)

If you have a better way, please post below in the YouTube comments.

Excel Most Efficient Way to REPTARRAY Challenge
(0:00) How to REPTARRAY
(0:51) JOIN, REPT, then SPLIT
(1:52) REDUCE, SEQUENCE, LAMBDA, VSTACK
(2:51) MAKEARRAY, LAMBDA, CHOOSEROWS, MOD
(3:56) FAST EXCEL V4
(4:56) Vote for REPTARRAY
(5:42) Nancy Faust