
Hi @gogi100
Generally, the options in Office apps, we are unable to remove, as they are by design.
Based on my knowledge, the ‘form-based sign-in' is an updated feature in Microsoft 365 apps that rolled out by the end of February 2020.
I suggest you open Office 2016 or 2019 apps on workstations both in work environment and test environment, go to File > Account > Product information, check the version numbers.
Please also go to Trust Center Settings > Trusted Locations, please add the documents path, you can also tick the box of 'Allow Trusted Locations on my network'.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.