Thank you! It works beautifully! And I understand the variables now.
I am using it like this in order to get mode=block:
<$transclude $tiddler="$year$ $mnth$ Journal Summary" $field="text" $mode="block"/>
UPDATE: It works beautifully on your website, but not in my wiki 
ON YOUR SITE
Even on your site, when I put <<newdiary 2024>> into a new tiddler, the month summary did not show up until I tagged your ExampleWithSummary tiddler (containing the summary define) with $:/tags/Macro … then the summary showed up even in the new tiddler.
IN MY WIKI
On my wiki, it is the $:/bj/macros/Calendar/diarydetsmacro that contains the summary define:
\define diarydets(i,tiddlerDate,rawDate,tags)
$i$<br>
<$list filter ="[tag[Journal]search:journal-date[$rawDate$]!is[system]]"><$link>{{!!journal-day-summary||journal-entry-summary}}</$link><br><$macrocall $name="image-basic" img={{!!journal-entry-thumbnail}} width="20%" align="" caption="" tooltip="" alt="" />
</$list>
\end
\define summarydets(mnth,year)
{{$year$ $mnth$ summary}}
\end
However even though that tiddler is tagged with $:/tags/Macro, no summaries are showing up in your calendars on my wiki.
I have your monthly calendar showing up on every month of Mohammed’s Journal-book (see this thread How can Journal Book be modified to show a Calendar if a Month is clicked - #10 by buggyj).
At first I thought that was somehow the complication but even when I created a simple new tiddler with nothing but <<newdiary 2024 7>> in it, it still does not show the summary. Even though $:/bj/macros/Calendar/diarydetsmacro is tagged with $:/tags/Macro.
So my wiki is at fault somehow, but as I can not share my personal wiki, I do not think I will be able to ask for help on it again until I have time to set up a tiddlyhost site with the Journal-Book combined with your calendar.
However thank you so much for what was solved, and maybe something will occur to me later.