list all values that begin with a specific letter

Hi, apologies for resurrecting that old thread.

The formula provided by AliGW in the previous thread about this isn't working for me. excelforum.com/excel-formulas-and-functions/1256982-list-all-values-that-begin-with-a-specific-letter.html#post5029367

I have a long list of 'names' (multiple words and single words e.g. 'Me Too', 'Tubbies on Telly' or 'Footing') on a sheet. For context this is a logbook of rock climbs in different places.
On a different sheet I want to list all cells that start with a specific letter that is entered in cell M1.

I modified Ali's formula to use my sheets =INDEX('all boulders'!$D$12:$D$7263,SMALL(IF(LEFT('all boulders'!$D$12:$D$7263,1)=$M$1,ROW('all boulders'!$D$12:$D$7263)),ROW(1:1))-1,1)
but it returns #VALUE! unless I make it an array formula by doing ctrl+shift+enter, at which point it returns a valid name from the list but this name does not start with the letter entered in cell M1. e.g. M1 = "J", result given is "Thriving Sincerity".

Is there some I'm missing here?

I have been generating similar lists from this data, returning the names based on what 'place' I select from a dropdown box using this formula:
=IFERROR(INDEX('all boulders'!$D$12:$D$7642,AGGREGATE(15,6,(ROW('all boulders'!$B$12:$B$7642)-ROW('all boulders'!$B$12)+ 1)/('all boulders'!$B$12:$B$7642 =$H$1), ROW('all boulders'!$A1))), "")
The value in $H$1 is the selected 'place' that I want the list of names to be at. i.e. 'Tubbies on Telly' is at a place called 'Fontainebleau'.
I am able to drag this formula down until it returns '0' when there are no more names listed as being in Fontainebleau.

I thought I might be able to modify this formula to list all names beginning with a specific letter by using the LEFT formula instead of the AGGREGATE formula but I can't get it to work.

I confess I am not knowledgable with excel formula. Up to now I have found answers to my problems by searching the web and manipulating the suggested solutions I find. e.g. I can't explain to you/anyone how the above formula works exactly but I kind of see what it is doing!

Apologies for the long, potentially confusing, post. I hope one of you amazing peeps can help me out.
Regards,
rew