There's no way for formulas to distinguish cells by formatting (other than some number formats) using only standard Excel functions. You could use VBA, but if you're new to Excel, that would be like having you proceed straight from single-digit arithmetic to multi-variable calculus. Even the contortions needed to be able to use number formatting would be like the jump from single-digit arithmetic to the quadratic formula.
Given your professed newness to Excel, you'd be better off inserting a column to the left of column A (select all of column A and insert a column, Excel will insert to the left), then entering x in the new col A cells for every boldface cell in new col B which would now have your original col A values. Then add the following formulas.
Fill F1 right as far as needed. It may be easier to copy F1 (move to cell F1, press [Ctrl]+C), then select, say, G1:K1, and paste (press [Ctrl]+V).
D2: =IFERROR(MATCH("?",INDEX(A:A,D1+1):A$1048576,0)+D1,2^20+1)
Select E1:K1, copy, and paste into E2:K2. Select D2:K2, copy, then select D3:Kn and paste, where n is a row number from 3 on depending on how many rows of results you need. The column D formulas will return 1048577 and columns E to K formulas #REF! when you've exhausted the text data in column B.
Yes, these are long and complex formulas. What you're doing is text processing. Excel can do it, but not easily. There are much better tools for doing things like this, e.g, most scripting languages if the source data had HTML boldface tags for the boldface lines.
Here's a link to an example in Excel Online.
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