Found this on PHP Manual (about PHP 8.x)
https://www.php.net/manual/en/language.oop5.magic.php#object.tostring

By removing force_xmlsettings_for_survey_rendering configuration, I got a similar error. That's because confinguration is an object.

Twig\Sandbox\SecurityNotAllowedMethodError

Calling "tostring" method on a "TemplateConfiguration" object is not allowed in "string_template__b85a9d86339e4b676595fbe968ac295f" at line 234.

To debug like this, i usually do var_export($var, true); https://www.php.net/manual/en/function.var-export.php
Maybe dump() function can ignore __toString() special method and use the var_export() function?
Also print_r($var, true); has the same behaviour https://www.php.net/manual/en/function.print-r.php

{{ dump() }} is something provided by Twig template engine, natively. (See: https://twig.symfony.com/doc/3.x/functions/dump.html)
By -not- declaring anything, will dump everything data available inside the template was called from.
In this situation, without passing arguments, it's able to display stringified objects, correctly.
Maybe it's time for Twig upgrade?

https://github.com/LimeSurvey/LimeSurvey/pull/4369

I'm not sure if this is a bug or not, because I don't think Lime uses the twig "dump" function anywhere.
But in many twig files, it is recommend to use dump for debugging.

I'm not sure if this is a bug or not, because I don't think Lime uses the twig "dump" function anywhere.

I already use it a lot !

Fix committed to master branch: http://bugs.limesurvey.org/plugin.php?page=Source/view&id=39007