VBA to make charts for a certain X,Y ranges and export slope results

I think, that instead of looking at parameters of trendline on the graph, it would be wiser just to calculate them.
In Excel you have two functions to do it: SLOPE and INTERCEPT. And to select only part of the data by limits in D or B column you can use FILTER function (good that you have Excel 2021, because it was not available in earlier versions).

And the limits shall be written in separate cells not as a range in one cell (see E4:F11 in attached file).
for 1st case (cells H7 and I7) the formulas would be:

Formula:

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and for H8:I8 and copied down for cases 2-5

Formula:

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And as for Graphs - if you would like to have graps too not just calculations, I'd think of making them dynamic in a similar way as presented just few threads ago https://www.excelforum.com/excel-for...-is-blank.html

You would need 10 names defined, 2 for each graph.

Final comment - if for different datasets you have different number of data points, think of maximum possible number - formulas could be with "surplus rows", like

Formula:

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just make sure you edit all max rows to the same number.

yet another ;-) final comment, of course you can use ROUND function and nest above formulas into it, to have results rounded to reasonable number of decimal places)