The "FTP" archive is also served over HTTPS nowadays, and has been for a long time. The hostname may still be ftp.funet.fi but there's an HTTP(S) server listening.
I'm actually a bit surprised that they do also seem to still run an actual FTP server there as well.
If you like working with old machines, you quickly learn to appreciate the availability of FTP servers. Encrypted connections are quite CPU intensive, particularly when negotiating the connection.
If you're working with something old enough for encrypted connections to be "CPU intensive", you're probably not talking to anything remotely current any way
TLS 1.3 is out there
TLS 1.2 is ubiquitious
I cannot recall the last time I saw anything older than TLS 1.1 anywhere - TLS 1.1 on down into the various SSL specs are all deprecated/unsupported[0]
TLS 1.1 and 1.0 have been deprecated for 2 years, SSL3 since 2015, SSL2 since 2011
If you're running something new enough to support TLS 1.1 (at least, 1.2 or 1.3 are much better), then the encryption overhead is very tiny
I'm actually a bit surprised that they do also seem to still run an actual FTP server there as well.