To address your concerns, one reason why you cant submit your response in microsoft forms is that you missed to answer a required question (s). Once a question is required (the one with red asterisk) the respondents are not allowed to submit unless the required questions were answered. I hope this will help you to resolve your concerns.
Check if clear IE cache and reset IE can resolve the issue. Open the Forms app on another computer with your account and check if the issue can be reproduced. Do all other users in your tenant have the same issue? What is your IE version and Windows version?
This of course begs the inquiry “Why can’t I upload my MS forms?”
Another answer is re: Failed to upload your file MS Forms Cause for this is because you’ve deleted the destination folder where you save the originally attachments. Also don’t delete the folder in a upper layer.
One of the next things we wanted the answer to was, why is the submit button greyed out in forms?
An answer is that if in case there are no required fields or these were answered and the submit button is greyed out, try refreshing the browser, clear the cache, resend the link of the form from the source. You may try also the suggestion of Neo Wu in this thread.
You are using the wrong link to the form. There are multiple links to access a form depending on what you are trying to do. You are using the Duplicate link which is designed to quickly create a form based on an existing form.
In the meantime, for those who could not access the Forms survey, please ask them to try the browser Internet Explorer or Edge if they could use PC. Also I suggest them switch a network (turn off VPN or proxy settings or Firewall if enabled).
Do I need an Office365 account to respond to a form?
As per Microsoft’s FAQ, it’s not mandatory to have an Office365 account in order to respond to a Forms. This thread is locked. You can follow the question or vote as helpful, but you cannot reply to this thread.
What is the root cause of Microsoft 365 authentication failure?
Preliminary root cause: A portion of infrastructure that manages authentication requests is degraded, affecting access to one or more Microsoft 365 services. Let us know if this helps!