I find the webpart is available in modern pages..

Here is a link, directly off the webpart:

https://formso365.nintex.com/webparthelp.html?SPLanguage=en-US

It is available but when you use it, can you successfully use the Display mode of the form? It always shows the Edit form for me.

There is a setting in the web part for the form mode. So getting display mode should be OK. One of the reasons I have not used this web part is the pain of getting the list item ID dynamically - which the web part needs, and I'm not sure how we can get this web part to consume a connection from a list view web part - which could provide a list item ID.