PHP Error using form Extension with Variants in TYPO3 11

i use the form extension (form) with variants and multiple steps for a contact form.
variants hide or show steps depending on the value of checkboxes or dropdowns.

the form works as expected but causes php-errors in the logs when i use php 8 or 8.1:

Core: Error handler (FE): PHP Warning: Undefined array key "singleselect-3-1-1" in /html/typo3/typo3_src-11.5.26/vendor/symfony/expression-language/Node/GetAttrNode.php line 97

in this case “singleselect-3-1-1” is the identifier of the field type: SingleSelect which is used as variant in the next step

TYPO3 11.5.26
form 11.5.26
PHP Version 8.0.26 or 8.1.13

Can anybody confirm this problem in TYPO3?
If yes, how can i submit this bug to the TYPO3 core team?
If no, i have to contact my hoster for a php problem?

Thanks for any feedback