CONFIG_PPPOE is not set in kernel config
ppp-pppoe package cannot be used. It needs the pppoe kernel module which is not compiled:
router [~]# ifup ppp0
Plugin rp-pppoe.so loaded.
PPPoE plugin from pppd 2.4.9
Cannot find device "ppp0"
Device "ppp0" does not exist.
router [~]# grep ppp /var/log/messages|tail -n 5
Apr 22 12:07:35 router daemon.info pppd[4334]: Plugin rp-pppoe.so loaded.
Apr 22 12:07:35 router daemon.info pppd[4334]: PPPoE plugin from pppd 2.4.9
Apr 22 12:07:35 router daemon.notice pppd[4336]: pppd 2.4.9 started by root, uid 0
Apr 22 12:07:35 router daemon.err pppd[4336]: Failed to create PPPoE socket: Protocol not supported
Apr 22 12:08:05 router daemon.err pppd[4336]: Failed to create PPPoE socket: Protocol not supported
router [~]# grep -i pppoe /boot/config-virt
# CONFIG_PPPOE is not set
router [~]# uname -a
Linux router 5.15.32-0-virt #1-Alpine SMP Mon, 28 Mar 2022 13:09:00 +0000 x86_64 GNU/Linux
router [~]#