COUNTIF() help I do not know how to make it working

Hi, I need a formula.

Column "B" has "names + surnames" with even homonyms & duplicated people.

Column "M" contains ONLY SURNAMES that I need to highlight if present in column “B”.

I want all the cells of column B, containing the single txt WORDS of the cells of column M, to be formatted with
bold PURPLE colour font.

The search must be of the text, among the single words in B, not of entire cells.
Column B contains 10.000 people with duplicates of with the same surname or even homonymous names.


I have been suggested to use the COUNTIF() function, to check if a text entry is found in another column as in the COUNTIF() formula the key is to use "*"& the search cell and another &"*" wildcard to search column B.
So, they suggested to make a new “N” or “helper” column and then to write this in N:

=COUNTIF($B$2:$B$10,"*"&M2&"*")
This counts if any part of M is found in B.
Then they said to use a formula in the conditional formatting FORMULA:
=O2=1
and apply to column B with FILL = PURPLE

Unfortunately I do not know where and how to input the COUNTIF() formula in coloum N
and I do not know where and how insert the formatting formula =O2=1
and where and how to apply to column B with FILL = PURPLE.

Can you help? Thanks, Max