How to extract multiple occurrences of a text enclosed between two same characters

Zdenek_Moravec 

Just to add some thoughts on modern Excel.  I am coming to be of the opinion that spreadsheet formulas are best presented as Lambda functions rather than having the formula details exposed.  In that case HansVogelaar's formula might be

ImportantText1λ
= LAMBDA(string,
    LET(
        newLine, CHAR(10),
        extracts, IFERROR(TRIM(TEXTAFTER(TEXTSPLIT(string, "<<"), ">>")),""),
        TEXTJOIN(newLine, TRUE, extracts, "")
    )
);

whilst mine might be

ImportantText2λ
= LAMBDA(string,
    LET(
        newLine, CHAR(10),
        regex, "[\w|\s]*(?=\<)",
        TEXTJOIN(newLine,,REGEXEXTRACT(string, regex, 1))
    )
);

The worksheet formulas would be

= MAP(notes, ImportantTextλ)

Any change to the formula made by the developer need not even be visible to the user (unless they are the same person of course) so the sheet may be updated when one chooses using the AFE (Advanced Formula Environment).