I’m not sure what do you mean by converting PCIe ports to Ethernet ports (RJ45). If you meant that you wanted to connect NIC cards to get Ethernet ports, then, I’ve the following questions.
Are you using JetsonAGX full setup (i.e. both module and I/O base board) or you have a custom designed IO board for the Jetson AGX module?
If you have a custom designed IO board where CEM form-factor PCIe slots are exposed, then, you can connect NIC cards to all those slots.
But, if you are using JetsonAGX base board, then, only x8 CEM slot is available to connect NIC cards (with PCIe CEM form-factor finger connector).
Other controllers have different kind of slots. For example,
One x1 controller has a SATA controller connected on-board so there is no slot exposed outside for this controller
One x1 controller has M.2 Key-E slot (to which typically only WiFi cards can be connected)
One x4 controller has M.2 Key-M slot (to which typically only SSD cards like NVMe storage can be connected)
Although we have a list of tested cards, any card with support available in the Linux kernel should just work as well.
You can try a card like https://www.amazon.com/StarTech-com-4-Port-Gigabit-Ethernet-Network/dp/B011NLWNHC?th=1 and connect to the x8 controller’s slot (the slot is a x16 slot BTW)
Hope this answer helps.