Please give the O365 version of the Nintex form the ability to connect to a list web part to filter in O365 the same way as its available in the On Prem Nintex forms as noted here: https://help.nintex.com/en-US/nintex2016/sp2016/Forms/SharePoint/ListFormWebpart.htm#:~:text=Use%20the%20Nintex%20Forms%20List,configure%20the%20web%20part%20directly.