I find an element by the following code:

self.document.xpath("//*[name()='desc']")

This element has brothers and sisters who do not have special characteristics to identify them and can only be recognized by their tags.

<g id="shape875-64" v:mID="875" v:groupContext="shape" transform="translate(43.0197,-65.2966)">
            <title>Sheet.875</title>
            <desc>ML_OP1</desc>
            <v:textBlock v:margins="rect(1,1,1,1)" v:tabSpace="42.5197" v:verticalAlign="0"/>
            <v:textRect cx="39.685" cy="243.262" width="79.38" height="17.0079"/>
            <rect x="0" y="234.758" width="79.3701" height="17.0079" class="st9"/>
            <text x="15.47" y="248.36" class="st11" v:langID="1033">ML_OP1</text>

</g>

Here I need last sibling <text>.

Note: I can only find objects using the string inside <desc> , that is, I find all the elements that have <desc> and then read the text inside them one by one and compare it with a dictionary.

If the mapping is done, I have to change the sibling element..

Now I need to find the sibling in one of the following two ways:
1- Finding parent and finding sibling through him
2- Finding sibling directly

I think my problem is that I can get everything by getting the first element xpath. If the element was among the selected objects, I could easily get its xpath in the loop(iterItems). But here no object is selected and my code is responsible for intelligently finding objects.

Sorry if it's a bit long. hope it is not complicated

selection_list = self.svg.selection

if len(selection_list) < 1:
    inkex.errormsg('Please select an object')
    return

next_object = selection_list[0].getnext()
previous_object = selection_list[0].getprevious()
if next_object != None:
    next_object_id = next_object.get_id()
else:
    next_object_id = 'none'

if previous_object != None:
    previous_object_id = previous_object.get_id()
else:
    previous_object_id = 'none'

inkex.errormsg(f'Next Object {next_object} Previous Object {previous_object}')
inkex.errormsg('---------------------')
inkex.errormsg(f'Next Object ID {next_object_id} Previous Object ID {previous_object_id}')