Here are the relevant paragraphs from the Catechism:
1398 The Eucharist and the unity of Christians. Before the greatness of this mystery St. Augustine exclaims, "O sacrament of devotion! O sign of unity! O bond of charity!"237 The more painful the experience of the divisions in the Church which break the common participation in the table of the Lord, the more urgent are our prayers to the Lord that the time of complete unity among all who believe in him may return.
1399 The Eastern churches that are not in full communion with the Catholic Church celebrate the Eucharist with great love. “These Churches, although separated from us, yet possess true sacraments, above all - by apostolic succession - the priesthood and the Eucharist, whereby they are still joined to us in closest intimacy.” A certain communion in sacris, and so in the Eucharist, "given suitable circumstances and the approval of Church authority, is not merely possible but is encouraged."238
1400 Ecclesial communities derived from the Reformation and separated from the Catholic Church, "have not preserved the proper reality of the Eucharistic mystery in its fullness, especially because of the absence of the sacrament of Holy Orders."239 It is for this reason that, for the Catholic Church, Eucharistic intercommunion with these communities is not possible. However these ecclesial communities, "when they commemorate the Lord’s death and resurrection in the Holy Supper . . . profess that it signifies life in communion with Christ and await his coming in glory."240
1401 When, in the Ordinary’s judgment, a grave necessity arises, Catholic ministers may give the sacraments of Eucharist, Penance, and Anointing of the Sick to other Christians not in full communion with the Catholic Church, who ask for them of their own will, provided they give evidence of holding the Catholic faith regarding these sacraments and possess the required dispositions.241
The key is whether the recipient holds the Catholic faith regarding the Eucharist, not whether they disagree on some other point of doctrine. In the case of Orthodox or the PNCC, the presumption is that they do, so the Church imposes no requirements beyond what it imposes on its own faithful. In the case of Protestants of whatever stripe, the presumption is that they don’t - so reception of the Eucharist is not permitted except in special circumstances when the situation is shown to be different.