There is a Minhag (custom) of eating garlic on Shabbat evening. Is this minhag also valid on Shabbat Yom Tov?
Seemingly, there should be no difference if the Friday evening is also Yom Tov.
There is a source in the talmud Baba Kama 82A ( בבא קמא פ״ב ) that ascribes eating garlic on friday evening to Ezra (one of his takonos- ordinances).
To quote: ושיהו אוכלין שום בע"ש משום עונה דכתיב (תהלים א, ג) אשר פריו יתן בעתו וא"ר יהודה ואיתימא רב נחמן ואיתימא רב כהנא ואיתימא ר' יוחנן זה המשמש מטתו מע"ש לע"ש
translated (sefaria) The Gemara explains the next of the ordinances that Ezra the Scribe ordained: And that one should eat garlic Shabbat eve. This is due to the fact that garlic enhances sexual potency, and Friday night is an appropriate time for conjugal relations. As it is written concerning the righteous: “And he shall be like a tree planted by streams of water, who brings forth his fruit in his season” (Psalms 1:3); and Rabbi Yehuda says, and some say it was Rav Naḥman, and some say it was Rav Kahana, and some say it was Rabbi Yoḥanan who said: This is referring to one who engages in sexual intercourse every Shabbat eve.