After successful Cross 64-Bit Toolchain Binary installation, you can easily test/cross-check/verify those binaries as follows:

• These 64-Bit Compiler Toolchain Binaries will only compile programs for Raspberry Pi Models/Versions with ARMV8-A CPU Architecture that supports 64-Bit execution state(You can find all supported Raspberry Pi Models here ) and with Raspberry Pi 64-Bit OS flavors(such as Pi64 by @bamarni ) installed.
• These instructions are exclusively for GCC 64-Bit Cross Compiler version 9.1.0 but will work with all 64-bit compiler versions available with this project.

Tip:bulb:: 'Right-Click' select 'Open image in new tab' to see the full-size image.

• Test GCC Support with aarch64-linux-gnu-gcc-9.1.0 -v command, check if the output is similar as follows:

cross 64 gcc

• Test G++ Support with aarch64-linux-gnu-g++-9.1.0 -v command, check if the output is similar as follows:

cross 64 g++

• Test GFORTRAN Support with aarch64-linux-gnu-gfortran -v command, check if the output is similar as follows:

cross 64 gfortran

• Test GDB Debugger Support with aarch64-linux-gnu-gdb -v command, check if the output is similar as follows:

cross 64 gfortran