The General Instruction of the Liturgy of the Hours has:
"239. During privileged seasons, if it is desired to celebrate the office of a saint on a day assigned to his or her memorial:
"a. in the office of readings, after the patristic reading (with its responsory) from the Proper of Seasons, a proper reading about the saint (with its responsory) may follow, with the concluding prayer of the saint;
“b. at morning prayer and evening prayer, the ending of the concluding prayer may be omitted and the saint’s antiphon (from the proper or common) and prayer may be added.”
Here I think it is referring to Optional Memorials and not Memorials. They are treated differently, as indicated by this part of the General Instruction of the Liturgy of the Hours:
“234. In the arrangement of the office there is no difference between obligatory and optional memorials, except in the case of optional memorials falling during privileged seasons.”
What is meant by “privileged seasons” in 239? I think anything that is not Ordinary Time, since there is a description of how Memorial are to be celebrated during Ordinary Time, beginning at n. 235.
So, for example, on 22 May 2020 the Optional Memorial of Saint Rita of Cascia may be celebrated in Morning Prayer, but only in the special way described in n. 239 b: “the ending of the concluding prayer may be omitted and the saint’s antiphon (from the proper or common) and prayer may be added.”
"Lord, hear our prayer: send out on all mankind the Spirit who makes us your sons, as foretold by Christ, the witness of your truth:
and so bring to completion through the gospel, the sanctification promised by your Word.
Whoever does the will of my Father, says the Lord, is my brother, and sister, and mother. Alleluia.
God our Father, you called Saint Rita of Cascia to seek your kingdom in this world by striving to live in perfect charity.
With her prayers to give us courage, help us to move forward with joyful hearts in the way of love.
We ask this though our Lord Jesus Christ, your Son, who lives and reigns with you in the unity of the Holy Spirit, one God, for ever and ever."
I have copied these texts from the Universalis App. It does not present them as I have shown.
For further research Fr McNamara’s article from Zenit may be helpful at https://www.ewtn.com/catholicism/library/commemorating-saints-in-lent-4516 and the UK General Instruction of the Liturgy of the Hours which has different translations than the ones I have put in this post https://www.liturgyoffice.org.uk/Resources/Rites/GILH.pdf .