Untrue. Orthodox Christians in good standing who believe in the real presence are able to receive Communion from a Catholic. That being said, most Orthodox bishops will advise their members against receiving communion from Catholics unless no Orthodox communion is available.
“Orthodox Christians in good standing who believe in the real presence are able to receive Communion from a Catholic.”
As said by Father Peter Sharpe of the Archdiocese of Fargo:
“When you say Amen and receive Communion at Mass, you are publicly declaring that you believe all that the Catholic Church teaches and believes. Further, you are acknowledging that you are trying to live as the Catholic Church expects. So if you don’t believe all that the Catholic Church believes or aren’t living according to her standards, when you receive Communion, it would be like you are publicly saying a lie, which of course you wouldn’t want to do.”
“Whereas many Protestant denominations allow Christians who are not members of their denominations to receive communion in their services, the Catholic Church does not.”
https://adoremus.org/2020/11/q-why-doesnt-the-catholic-church-share-communion-with-non-catholics/
And it goes the other way, also, according to what I have found:
“According to the Code of Canon Law, receiving communion in a Protestant church is generally not permissible. According to canon 844, “Catholic ministers may licitly administer the sacraments to Catholic members of the Christian faithful only and, likewise, the latter may licitly receive the sacraments only from Catholic ministers.” The key term here is licit. If a Catholic receives communion from a Protestant minister, it is generally considered “illicit” or unlawful.”
https://uscatholic.org/articles/201108/can-a-catholic-receive-communion-in-a-protestant-church/
There appears to be a mixed bag on this subject.
wy69