Enable External RDP Access To One Of My Desktop PCs

Seems more of an administrative rather than technical issue, but I will try asking here anyway.

All I need to do is be able to reach one of my desktop PCs and remote control it using Microsoft Remote Desktop Protocol (RDP).

I am an Xfinity customer based in Grand Rapids, MI and have my own equipment, including:

1. Arris Surfboard SB6183 Cable Modem
2. TP-Link Archer C3200 Internet Router

My desktop is a Dell Inspiron 3880, an i5-based PC running Windows 11 Pro (24GB RAM, 240GB SSD, 5TB HDD).

My main problem seems to be that my external IP address is "hidden" outside my home network. I can ping it from the PC I want to allow RDP access to, but I cannot reach it from anywhere else outside (e.g. at a Starbucks or at a friend's house or anywhere else).

I have already added a port-forwarding rule in my router to the specific PC I need to connect to. I do not, however, use a VPN...  I'd rather not go that route if I don't have to.

I tried contacting Xfinity support 5 different times (4 calls and one visit to a nearby store) and no one seemed to even grasp what I just described above.

Any competent help would be greatly appreciated.