This will work with the gnu version of sed ( by default on every linux )
echo -n '#HelloMyName@#IsAdam@#NiceToMeetYou@' | sed 's/#\([^@]*\)@/\1\n/g'
give me
HelloMyName
IsAdam
NiceToMeetYou
On macos
echo '#HelloMyName@#IsAdam@#NiceToMeetYou@' | sed 's/#\([^@]*\)@/\1\'$'\n''/g'