Hi!
The URL should be a bit different:
$ lxc remote add faster https://free.nchc.org.tw/ubuntu-cloud-images/releases/server --protocol simplestreams
$ lxc init faster:c mycontainer
Retrieving image: metadata: 100% (1.26GB/s)
Retrieving image: rootfs: 2% (810.06kB/s)
Error: Remote operation canceled by user
$
That is, for free.nchc.org.tw, the URL for lxc remote should instead be https://free.nchc.org.tw/ubuntu-cloud-images/releases/server