https://www.aliyousefian.com/1007/ecdsa-public-key-compression-in-erlang/

compress_ecdsa_publickey.erl

-module(compress_ecdsa_publickey).
-export([compress_ecdsa_publickey/1, test/0]).

compress_ecdsa_publickey(UncompressedPublicKey) ->
    %% To binary
    UncompressedPublicKeyBin = binary:decode_hex(list_to_binary(UncompressedPublicKey)),
    %% Check that the uncompressed public key is valid
    case size(UncompressedPublicKeyBin) of
        65 ->
            %% Remove the prefix (first byte) from the public key
            PublicKey = binary:part(
                UncompressedPublicKeyBin, 1, byte_size(UncompressedPublicKeyBin) - 1
            ),
            %% Extract the x-coordinate
            X = binary:part(PublicKey, 0, 32),
            %% Extract the y-coordinate
            Y = binary:part(PublicKey, 32, 32),
            %% Extract the y-coordinate last byte
            YLastByte = binary:last(Y),
            %% Determine whether the y-coordinate is even or odd
            case YLastByte rem 2 of
                0 -> Prefix = <<2>>;
                1 -> Prefix = <<3>>
            end,
            %% Concatenate prefix and x to obtain the compressed public key
            CompressedPublicKey = <<Prefix/binary, X/binary>>,
            {ok, binary_to_list(binary:encode_hex(CompressedPublicKey))};
        _ ->
            io:format("Invalid public key ~p, The public key has length of: ~p", [
                UncompressedPublicKey, size(UncompressedPublicKeyBin)
            ]),
            error
    end.

test() ->
    UncompressedPublicKey = "0479be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08ffb10d4b8",
    %% Call the compress_ecdsa_publickey function
    compress_ecdsa_publickey(UncompressedPublicKey).