2017 - 2019 titans have a different part number for the frame assembly as compared to the 2020 - 2023 version. I have no idea what the differences are as the pictures look exactly the same to me, but I assume there has to be some difference.

2017-2019 Nissan TITAN Frame Assembly 50100-EZ23A | Nissan Parts Plus

2020-2023 Nissan TITAN Frame Assembly 50100-9FV1A | Nissan Parts Plus

 

2017 - 2019 titans have a different part number for the frame assembly as compared to the 2020 - 2023 version. I have no idea what the differences are as the pictures look exactly the same to me, but I assume there has to be some difference.

If I had to guess they are different where the transmission mount to the frame since the 2017-19 use the 7 speed and the 2020-24 use the 9 speed.
2017-2019 Nissan TITAN Frame Assembly 50100-EZ23A | Nissan Parts Plus

2020-2023 Nissan TITAN Frame Assembly 50100-9FV1A | Nissan Parts Plus

 

I believe the frame was modified somewhat for crash worthiness. The XD appears to be very similar '19 - '20, except for some cross members towards the front of the truck. I would assume the same is true for the non-XD trucks.