PHP Warning: Undefined array key

Hi there ??</img> 

First of all, thank you for this very useful plugin ??</img> 
Currently I have 2 warnings in my debug with emails that do not leave:

PHP Warning:  Undefined array key "placeholder" in ~/wp-content/plugins/multiple-post-passwords/admin/settings-page.php on line 214
PHP Warning:  Undefined array key "min" in ~/wp-content/plugins/multiple-post-passwords/admin/settings-page.php on line 206

And I noticed that in the instructions and my navigator console (from the plugin Settings), the instructions for the field “Expire passwords after x hours” are with a separation point while the entered figure is systematically transformed with a comma (via the arrows too):

Screenshot here:

https://markuphero.com/share/MnfldzuaR9oKWfjHGAlf

Thank you for your help!

Warm regards,
Ludovic

PS: I use PHP 8.0, maybe it affects?

EDIT: I just put a round figure (1 hour) and when saving the settings, the same warnings appear all the same (strong to bet that the stories of commas and points have nothing to do so)