If you have Office 365 and access to functions (SEQUENCE,TEXTJOIN) then for Zeroes the formula would be:
=TEXTJOIN(",",TRUE,IF(MID($A2,SEQUENCE(99,1,1,1),1)="0",SEQUENCE(99,1,1,1),""))
For O Letter:
=TEXTJOIN(",",TRUE,IF(MID($A2,SEQUENCE(99,1,1,1),1)="O",SEQUENCE(99,1,1,1),""))