The Canon Speedlite EL-5 is not compatible with the Canon EOS 6D Mark II. This is because the Speedlite EL-5 uses the new Multi-Function Shoe, which is only compatible with selected Canon EOS R Series camera bodies such as the EOS R6 Mark II, EOS R7, EOS R10 and EOS R3 and not with older cameras that use a different hot shoe design.

The Canon EOS 6D Mark II would require a different flash unit that is compatible with the older hot shoe design. An example of this would be the Canon Speedlite 430EX III-RT or the Canon Speedlite 600EX II-RT, which are compatible with the EOS 6D Mark II and offer good quality.