What is the value you are expecting compared to the value you are actually getting?
Are additional values being exported to excel? Are there missing values?
Could be a rounding issue.

I built a form to test your code and I got the correct total.

Hi Kevin,
The differences increase as the list get longer.
The export list is identical to the list box list in Access
I also defined the roundings in the Qwery to "2" after the comma
I added some screenshots to this answer.

It may be the Column Heads causing the problem.
Try changing the Lower Bound value to 1 instead of 0.

For i = 1 To SearchboxDBOrders.ListCount - 1

I tried but has no effect.
But I have started to think about your remarks about roundings after the decimal point.
I noticed that my result always ends at ###, 00 while I did expect a number after the decimal point.
I discussed this with ChatGTP and it asked me to change the code as below:

Dim SumSelectedOrders As Currency ' Use Currency for precision with decimals
       SumSelectedOrders = 0

Dim i As Long

For i = 0 To SearchboxDBOrders.ListCount - 1
    SumSelectedOrders = SumSelectedOrders + CCur(SearchboxDBOrders.Column(4, i)) ' Custom column index as needed
Next i

TxtTotalSelectedOrders.Value = SumSelectedOrders

But then Access informed me that the types are mismatch.
I also try to look for solutions, but I can't figure it out yet.

Hi Bruno, in your original code, the Val() function does not recognize commas "," as part of a number.  Val() only looks at the numeric portion at the start of the entry, and ignores anything after the comma.  Therefore, all the decimals in your numbers are ignored, and that is why you get an incorrect total.

If the text does not begin with a number, such as "EUR 100", Val() will simply ignore everything and return zero.  Due to all these caveats, Val() is not really the function to do conversions in many cases.  (I use it mainly for sorting alphanumeric data, actually.)

CCur() also doesn't work because it requires a number (or string) that looks exactly like a literal number.  And yours don't, because they have spaces.  For instance, CCur("27 250") won't work, but CCur("27250") will.

I would suggest you use a subform instead of a listbox.  A subform can require a field to be numeric, thus assuring of the correct math being used for the total.  A listbox, however, contains only text.  A subform also lets you format a numeric field to whatever appearance you like (see picture below).