Calender pop-up not available for some users

Hello, I am running c5 9.1.3 with PHP 8.0 (but the problem remained when using PHP7.4).
Some users want to send a form but one field where you have to obligatorily enter a date is zeroed and the form cant be send. This happens with differnt browser but only for some users, other can send the form and everything is fine.
What I could observe is that the problem happens if the calender popup is not shown/loaded/displayed.
Could the use pop-up-blockers be responsible for this or what else could be the reason?
Thanks in adavance

I meanwhile found that Admins have the expected functionality - calender pop-up working and report gets sent - but all users who have no permissions to edit the page with the form dont get the pop-up and they cant send the form. Does anyone know why this is happening?

Hello again, no one who could help me with my problem? If I use the field type date in a simple form block, it only works as Admin to send the form and enter a date. No other user groups can send the form, instead they get an error message that the date has to be entered, although they entered it before.

Hi @Lovic - is this a standard install? If you spin up a demo site here can you recreate the problem?