Concatenate or vlookup or something else?

=LET(range,A1:O9,
database,VSTACK(HSTACK("",DROP(TAKE(range,1),,1)),FILTER(DROP(range,1),
BYROW(DROP(range,1,1),LAMBDA(x,SUM(N(x="x")))))),
IFNA(DROP(REDUCE("",SEQUENCE(ROWS(DROP(database,1))),LAMBDA(u,v,
VSTACK(u,
LET(
rng,TRANSPOSE(VSTACK(TAKE(DROP(database,,1),1),CHOOSEROWS(DROP(DROP(database,,1),1),v))),
a,SCAN(0,INDEX(rng,,2),LAMBDA(ini,arr,IF(arr="x",ini+1,0))),
b,VSTACK(DROP(a,1),0),c,VSTACK(0,DROP(a,-1)),
mapend,MAP(a,b,LAMBDA(aa,bb,IF(AND(aa>1,bb=0),1,0))),
mapstart,MAP(a,b,c,LAMBDA(aaa,bbb,ccc,IF(AND(aaa=1,bbb=2,ccc=0),1,0))),
start,FILTER(CHOOSECOLS(rng,1),mapstart),
end,FILTER(INDEX(rng,,1),mapend),
nonconsecutive,FILTER(INDEX(rng,,1),(a=1)*(b=0)),
dates,VSTACK(IFERROR(nonconsecutive,""),IFERROR(HSTACK(start,"- "&TEXT(end,"TT.MM.JJJJ")),"")),
filtereddates,FILTER(dates,LEN(INDEX(dates,,1))>0),
sorteddates,SORTBY(filtereddates,INDEX(filtereddates,,1),1),
HSTACK(INDEX(DROP(TAKE(database,,1),1),v),sorteddates))))),1),""))

Hello Dawn-Marie,

you are welcome. Unfortunately i didn't understand what you exactly want to do. I was only focussing on consecutive dates which are at least two dates in a row in my understanding. The new formula in addition works if there is only one date like for August or if there isn't any date as for June in my example.