May Notes contain emoji graphics?
There is a patch to support the character encoding necessary: https://lab.civicrm.org/dev/core/issues/339.

The issue is whether to support older character sets for folks who can't/won't switch over.  One position is that it's not a big ask for users to upgrade, but difficult for the developers to support both; the other position is that it forces an update that some folks can't make, or that their database is too big to convert without going offline for several hours.

The "support the new encoding only" patch has been written; this will move forward either when a) someone writes a patch that supports both encodings, or b) folks decide it's OK to force folks to switch.