Zrjydtj

As stated, I wonder if there is any possibility to dynamically add items to a list and print it anywhere in the document, regardless of where the definitions are made.

I'm thinking something like this:

documentclass[a4paper,12pt]article
defineListMyListName
begindocument
beginitemize
printlistMyListName
enditemize
Lorem ipsum dolor sit amet...
addToListMyListNameitem First
addToListMyListNameitem Second
enddocument

and this would then result in something like this (in essence, the printlistMyListName merely acts as a macro and is replaced by the content of the list:

Of course, being able to iterate over the list items would be even more elegant, however it might introduce too much complexity.

You can use the .aux file.

With defineList we initialize a sequence variable; each addToList command writes in the .aux file the corresponding entry as argument to chrillofaddtolist.

When the .aux file is read in at begin document, the sequence is populated with the items gathered in the previous run so it will be available as soon as the document starts.

The command chrillofaddtolist is made a no-op at end document, when the .aux file is read back in, but we need no action.

Finally, printList just delivers the sequence.

As a technical workaround, I added a litemize environment, so no error is raised when the sequence is still empty.

documentclass[a4paper,12pt]article
usepackagexparse

ExplSyntaxOn
NewDocumentCommanddefineListm
 
 seq_new:c g_chrillof_list_#1_seq 
 
NewDocumentCommandaddToListmm
 
 iow_shipout:cn @auxout chrillofaddtolist #1 #2 
 
NewDocumentCommandchrillofaddtolistmm
 
 seq_gput_right:cn g_chrillof_list_#1_seq #2 
 
NewDocumentCommandprintListm
 
 seq_use:cn g_chrillof_list_#1_seq 
 
AtEndDocumentcs_set_eq:NN chrillofaddtolist use_none:nn 
ExplSyntaxOff

makeatletter
newenvironmentlitemize
 let@noitemerrrelaxitemize
 enditemize
makeatother

defineListMyListName

begindocument

beginlitemize
printListMyListName
endlitemize

Lorem ipsum dolor sit amet...

addToListMyListNameitem First
addToListMyListNameitem Second

enddocument

The sagetex package, documentation here, gives you access to the Python programming language. This is one way to keep track of the list and print using a loop.

documentclassarticle
usepackagesagetex
begindocument
beginsagesilent
MyList = ["spring","summer"]
output = r"beginitemize"
for i in range(0,len(MyList)):
 output += r"item %s"%(MyList[i])
output += r"enditemize"
endsagesilent

sagestroutput

Lorem ipsum dolor sit amet...

beginsagesilent
MyList.insert(0,"winter")
MyList.append("fall")
output = r"beginitemize"
for i in range(0,len(MyList)):
 output += r"item %s"%(MyList[i])
output += r"enditemize"
endsagesilent

sagestroutput
enddocument

The result is shown below:

The "behind the scenes" work is done in sagesilent environment. The original list is created to contain "spring" and "summer". A for loop creates a string that will put the list into the itemize environment. To insert it into the document, use sagestr, the SAGE string environment. If we want to add "winter" to be first in the list and "fall" to be last, the command MyList.insert(0,"winter") puts "winter" in the first position (which in Python is the zeroth position). The command MyList.append("fall") puts "fall" at the end of the list, however long it is. The for loop prints out over the longer list since len(MyList) is the length of the list.

The extra block of code each time is a bit clunky but it is easy to read and modify. You also get the benefit of being able to insert into any part of the list. The sagetex package relies on the computer algebra system SAGE, which is not part of the LaTeX package. It either needs to be downloaded to your computer or you can open a free Cocalc account and work from the cloud.

Requires two passes. Based on my answer at Extracting the structure of a LaTex document, including comments, but adapting the syntax to meet the OP's needs.

Multiple lists can be simultaneously active. Here, in the MWE, I build "xyz" and "pdq" lists.

documentclassarticle
letsvaddtocontentsaddtocontents
makeatletter
newcommanddefineList[1]%
 expandafterdefcsname add#1lineendcsname##1##2##3addtocontents ##1%
 protect csname #1lineendcsname ##2##3
 expandafterdefcsname write#1endcsname%
 renewcommandaddtocontents[2]relax%
 setcountersection0noindent%
 expandafterdefcsname #1lineendcsname####1####2expandaftercsname####1endcsname####2%
 @starttoc#1%
 setcountersection0%
 letaddtocontentssvaddtocontents%
 %
 csname add#1lineendcsname#1beginitemize%
 AtEndDocumentcsname add#1lineendcsname#1enditemize

newcommandaddToList[2]csname add#1lineendcsname#1item#2
newcommandprintList[1]csname write#1endcsname
makeatother
begindocument
%tableofcontents% CAN UNCOMMMENT TO SEE THAT toc WORKS FINE
defineListxyz
defineListpdq

sectionIntroduction

addToListxyzFirst item on my list.
Text related to why tracking balls is important, blah, blah, blah. 
Blah, blah, blah. 
addToListpdqFirst pdq item

Here is my XYZ list:
printListxyz

sectionNext Section

addToListxyzSecond item on list
Text relating the challenges, blah, blah, blah. 
More blah, blah, blah.
addToListpdqNext pdq item 

addToListxyzThird item on list.
Here is my PDQ list:
printListpdq

Text relating the existing work on tracking balls, blah, blah, blah. 
Blah, blah, blah.

enddocument