Hi and welcome to the forum:
Sadly, RF lenses are not compatible to DSLRs, of which your EOS 77D is an example, and there are no adapters to be able to combine them.
If you want something of similar reach, either a Sigma or Tamron 150-600 lens would actually render a similar image result. Because the 77D has an APS-C crop sensor, it captures a smaller Field of View (what the sensor actually records) than the Full Frame sensors. This gives the resultant image an apparent magnification boost, that would be Equivalent to a lens 1.6x longer than the same lens on a FF camera. Thus a Sigma 150-600c, combined with the smaller Canon APS-C sensor of your 77D would yield an image equivalent to that of a 240-960mm lens on a FF body.
Such a lens is probably your best bet. I have shot with the Sigma 150-600c quite an lot and it is an excellent optic on both FF and ASP-C crop cameras.
cheers, TREVOR
The mark of good photographer is not what they hold in their hand, it's what they hold in their head;
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
