As you may or may not have noticed, both `ppp` and `rp-pppoe` package
used to ship a `rp-pppoe.so` and they are not 100% compatible. Back in
2021, ppp 2.4.9 starts to rename its own copy of `rp-pppoe.so` to
`pppoe.so`. As of `ppp 2.5.0`, upstream decided to remove the
`rp-pppoe.so` symlink and thus broke configurations with the old name.

If you still have the old ppp package's `rp-pppoe.so` configured
somewhere (likely in /etc/ppp/peers/), please update it to use just
`pppoe.so`. Configurations with the same plugin from the `rp-pppoe`
package (using full path like /usr/lib/rp-pppoe/rp-pppoe.so) are not
affected.