Ubuntu Linuxには、arm64(aarch64) 用のクロス開発ツールのパッケージが用意されていますので、
それをセットアップします。

user1@max3xx-devel:~$ sudo apt install crossbuild-essential-arm64
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following additional packages will be installed:
  binutils-aarch64-linux-gnu cpp-11-aarch64-linux-gnu cpp-aarch64-linux-gnu cross-config dpkg-cross file
  g++-11-aarch64-linux-gnu g++-aarch64-linux-gnu gcc-11-aarch64-linux-gnu gcc-11-aarch64-linux-gnu-base
  gcc-11-cross-base gcc-12-cross-base gcc-aarch64-linux-gnu libasan6-arm64-cross libatomic1-arm64-cross
  libauthen-sasl-perl libc6-arm64-cross libc6-dev-arm64-cross libclone-perl libconfig-auto-perl
  libconfig-inifiles-perl libdata-dump-perl libdebian-dpkgcross-perl libencode-locale-perl libfile-homedir-perl
  libfile-listing-perl libfile-which-perl libfont-afm-perl libgcc-11-dev-arm64-cross libgcc-s1-arm64-cross
  libgomp1-arm64-cross libhtml-form-perl libhtml-format-perl libhtml-parser-perl libhtml-tagset-perl
  libhtml-tree-perl libhttp-cookies-perl libhttp-daemon-perl libhttp-date-perl libhttp-message-perl
  libhttp-negotiate-perl libhwasan0-arm64-cross libio-html-perl libio-socket-ssl-perl libio-string-perl
  libitm1-arm64-cross liblsan0-arm64-cross liblwp-mediatypes-perl liblwp-protocol-https-perl libmagic-mgc libmagic1
  libmailtools-perl libnet-http-perl libnet-smtp-ssl-perl libnet-ssleay-perl libstdc++-11-dev-arm64-cross
  libstdc++6-arm64-cross libtimedate-perl libtry-tiny-perl libtsan0-arm64-cross libubsan1-arm64-cross liburi-perl
  libwww-perl libwww-robotrules-perl libxml-libxml-perl libxml-namespacesupport-perl libxml-parser-perl
  libxml-sax-base-perl libxml-sax-expat-perl libxml-sax-perl libxml-simple-perl libyaml-libyaml-perl libyaml-perl
  linux-libc-dev-arm64-cross perl-openssl-defaults
Suggested packages:
  binutils-doc gcc-11-locales cpp-doc binutils-multiarch gcc-11-doc autoconf automake libtool flex bison
  gdb-aarch64-linux-gnu gcc-doc libdigest-hmac-perl libgssapi-perl libcrypt-ssleay-perl libsub-name-perl
  libbusiness-isbn-perl libauthen-ntlm-perl libxml-sax-expatxs-perl libyaml-shell-perl
The following NEW packages will be installed:
  binutils-aarch64-linux-gnu cpp-11-aarch64-linux-gnu cpp-aarch64-linux-gnu cross-config crossbuild-essential-arm64
  dpkg-cross file g++-11-aarch64-linux-gnu g++-aarch64-linux-gnu gcc-11-aarch64-linux-gnu
  gcc-11-aarch64-linux-gnu-base gcc-11-cross-base gcc-12-cross-base gcc-aarch64-linux-gnu libasan6-arm64-cross
  libatomic1-arm64-cross libauthen-sasl-perl libc6-arm64-cross libc6-dev-arm64-cross libclone-perl
  libconfig-auto-perl libconfig-inifiles-perl libdata-dump-perl libdebian-dpkgcross-perl libencode-locale-perl
  libfile-homedir-perl libfile-listing-perl libfile-which-perl libfont-afm-perl libgcc-11-dev-arm64-cross
  libgcc-s1-arm64-cross libgomp1-arm64-cross libhtml-form-perl libhtml-format-perl libhtml-parser-perl
  libhtml-tagset-perl libhtml-tree-perl libhttp-cookies-perl libhttp-daemon-perl libhttp-date-perl
  libhttp-message-perl libhttp-negotiate-perl libhwasan0-arm64-cross libio-html-perl libio-socket-ssl-perl
  libio-string-perl libitm1-arm64-cross liblsan0-arm64-cross liblwp-mediatypes-perl liblwp-protocol-https-perl
  libmagic-mgc libmagic1 libmailtools-perl libnet-http-perl libnet-smtp-ssl-perl libnet-ssleay-perl
  libstdc++-11-dev-arm64-cross libstdc++6-arm64-cross libtimedate-perl libtry-tiny-perl libtsan0-arm64-cross
  libubsan1-arm64-cross liburi-perl libwww-perl libwww-robotrules-perl libxml-libxml-perl
  libxml-namespacesupport-perl libxml-parser-perl libxml-sax-base-perl libxml-sax-expat-perl libxml-sax-perl
  libxml-simple-perl libyaml-libyaml-perl libyaml-perl linux-libc-dev-arm64-cross perl-openssl-defaults
0 upgraded, 76 newly installed, 0 to remove and 0 not upgraded.
Need to get 61.0 MB of archives.
After this operation, 222 MB of additional disk space will be used.
Do you want to continue? [Y/n] 

ARM64 用 GCC の起動を確認してみます。