Adding a whole ipv6 /64 block to a ubuntu 18.04 server

Question

I know there are other questions that had already asked this, but the solutions don't work (anymore and for me).

I added the IP in the netplan config file(01-netcfg.yml):

  version: 2
  renderer: networkd
  ethernets:
    eth0:
      addresses: [37.xxx.xxx.4/22, "2a03:xxxx:xxxx:xxxx::1/64", "92.xxx.xxx.xxx/22"]
      gateway4: 37.xxx.xxx.1
      gateway6: fe80::1
      nameservers:
        addresses: [46.xxx.xxx.230, 46.xxx.xxx.230, "2a03:xxxx:xxxx:xxxx::e1e6", "2a03:xxxx:xxxx::xxxx", "1.1.1.1"]

This configuration does work, but it only makes this one IP (2a03:xxxx:xxxx:xxxx::1) available. There must be way to assign the whole IP block the the network card, but I can't figure it out...