Yep. Under normal circumstances. Ditto for Communion - that’s why I brought up canon 844… I was just surprised you didn’t bring out this canon since the OP’s post was on Communion and I said not to receive Communion from the Orthodox (which is a general rule of thumb) and this is one of those pesky exceptions!!! Anyway, don’t want to get off topic. Just that I am aware of certain cases in which there is a possibility the obligation is actually fulfilled in an Orthodox church, but they’d be pretty rare. God bless!
I am not aware of
any case where the Sunday or Holy Day or communion obligation is fulfilled in a non-Catholic Church. Ecumenical events are to be scheduled in addition to the normal Sunday or Holy Day liturgies. There is obligation to receive communion for a Catholic according to the laws of the Church
sui iuris (CCEO 708, CIC 920). If it is physically or morally impossible to receive communion per these canons, then the obligation for Catholics, is not binding. Also, Catholics are not required to go to a non-Catholic Church.
DIRECTORY FOR THE APPLICATION OF PRINCIPLES AND NORMS ON ECUMENISM has: 115. Since the celebration of the Eucharist on the Lord’s Day is the foundation and centre of the whole liturgical year,120 Catholics—but those of Eastern Churches according to their own Law 121—are obliged to attend Mass on that day and on days of precept.122 It is not advisable therefore to organize ecumenical services on Sundays, and it must be remembered that even when Catholics participate in ecumenical services or in services of other Churches and ecclesial Communities, the obligation of participating at Mass on these days remains.
120 Cf.
Sacrosanctum Concilium, n. 106.
121 Cf. CCEO, can. 881, 1; CIC, can. 1247.
122 Cf. CIC, can. 1247; CCEO, can. 881, 1.
vatican.va/roman_curia/pontifical_councils/chrstuni/general-docs/rc_pc_chrstuni_doc_19930325_directory_en.html
Sacrosanctum Consilium, No. 106Accordingly the sacred Council has seen fit to decree as follows.
- By a tradition handed down from the apostles which took its origin from the very day of Christ’s resurrection, the Church celebrates the paschal mystery every eighth day; with good reason this, then, bears the name of the Lord’s day or Sunday. For on this day Christ’s faithful are bound to come together into one place so that; by hearing the word of God and taking part in the eucharist, they may call to mind the passion, the resurrection and the glorification of the Lord Jesus, and may thank God who “has begotten them again, through the resurrection of Jesus Christ from the dead, unto a living hope” (1 Pet. 1:3). Hence the Lord’s day is the original feast day, and it should be proposed to the piety of the faithful and taught to them so that it may become in fact a day of joy and of freedom from work. Other celebrations, unless they be truly of greatest importance, shall not have precedence over the Sunday which is the foundation and kernel of the whole liturgical year.
vatican.va/archive/hist_councils/ii_vatican_council/documents/vat-ii_const_19631204_sacrosanctum-concilium_en.html