For the benefit of others stumbling upon this, this is how my configuration was converted to the new format.
old configuration in /etc/ser2net.conf:
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BANNER:hikey01:\r\nser2net - hikey01
2000:telnet:600:/dev/serial/by-id/usb-FTDI_TTL232RG-VREG1V8_FT1UKFGA-if00-port0:115200
8DATABITS NONE 1STOPBIT hikey01 max-connections=2
----------------8<----------------8<----------------8<-----------------
new configuration in /etc/ser2net.yaml:
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connection: &hikey01
accepter: tcp,2000
enable: on
options:
banner: "ser2net - hikey01\r\n\r\n"
kickolduser: false
telnet-brk-on-sync: true
max-connections: 2
connector: serialdev,
/dev/serial/by-id/usb-FTDI_TTL232RG-VREG1V8_FT1UKFGA-if00-port0,
115200n81,local
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