You can easily adapt this script to download the IPv6 bogon list, if the list is shorter than the max variable length!

• Download CA certificates and upload to RouterOS, or with next command (not encrypted by TLS!):

  /tool fetch url=https://curl.se/ca/cacert.pem

• Import certificates:

  /certificate import file-name=cacert.pem passphrase=""

• Create a new script:

  /system script add name=bogons

• Edit new script:

  /system script edit [/system script find name=bogons] source

• Paste script:

  # Automatically add BOGONs to your firewall's address lists.
  # Only works with 6.43 and up.
  #
  # Please do not fetch more often than the listed update interval, for the 
  # lists that are updated only as IANA allocations change, please do not fetch 
  # more than once per day.
  #
  # by Phillip Stromberg
  # 2018-11-07
  # uses team-cymru.org BOGON lists
  {
      :global content;
      :local url;
      :local addressListName;
      
      :set addressListName "AUTOBOGON"
      
      ####################### UNCOMMENT THE URL YOU NEED: #######################
      
      ### This is the list of bit notation bogons, aggregated, in text format.
      ### Updated as IANA allocations and special prefix reservations are made.
      
      # :set url "https://www.team-cymru.org/Services/Bogons/bogon-bn-agg.txt"
      
      ### The traditional bogon prefixes, plus prefixes that have been allocated to RIRs 
      ### but not yet assigned by those RIRs to ISPs, end-users, etc.
      ### Updated every four hours.
      
      :set url "https://www.team-cymru.org/Services/Bogons/fullbogons-ipv4.txt"
      
      ###########################################################################
      
      :local result [/tool fetch url=$url as-value output=user];
      
      :if ($result->"status" = "finished") do={
          :set content ($result->"data");
      }
      :global contentLen [ :len $content ];
      :global lineEnd 0;
      :global line "";
      :global lastEnd -1;
      
      /ip firewall address-list remove [find list=$addressListName];
      
      :do {
          :set lineEnd [:find $content "\n" $lastEnd ];
          :set line [:pick $content $lastEnd $lineEnd];
          :set lastEnd ( $lineEnd + 1 );
          :if ( [:pick $line 0] = "#" ) do={
          } else={
              # :put $line;
              /ip firewall address-list add address=$line list=$addressListName;
          }
          
      } while=($lineEnd < $contentLen - 2)
  }
  

• Set policy:

  /system script set bogons policy=read,write,test

• Test run script:

  /system script run bogons

• Schedule script:

  /system scheduler add interval=1d on-event=bogons name=update-bogons

• Add firewall rules with:

  dst-address-list=!AUTOBOGON