The primary obstacle to official rtl8196e openwrt support has always been, paradoxically, Realtek themselves. To get their hardware functional, Realtek took a very old (circa 2013) version of the Linux kernel, heavily modified it to support the RTL819x series, and then never contributed these changes back to the mainline Linux kernel.
RTL8196E boards may require specific drivers ( kmod-rtk-rtl8192er or similar) to be enabled or installed via SSH. rtl8196e openwrt