Aglae

Aymeric

Blandine

Celestine is a pretty, crystalline extension (actually a diminutive) of Celeste that would make a choice that is both delicate and strong. It is also a popular name in France.
 Celestine was the name of painter Edgar Degas's Creole mother. Some people might associate it with the 1993 spiritual novel "The Celestine Prophecy."
 Celestina is another attractive version.

Celestine

A romantic rarity, derived from the Old German name Chlotichilda, meaning "famous in battle." Saint Clotilde was a Frankish queen, wife of Clovis I, who played a role in the spread of Christianity.

Clotilde

Clovis

Colombe

Constance is one of the more subtle of the virtue <a href="https://nameberry.com">baby names</a>, but still has quite a prim and proper image. One impediment to its revival has been the decidedly dated nickname Connie, though modern parents might well opt for using the strong and dignified name in full.
 One of William the Conqueror's daughters was named Constance, and in Shakespeare's King John, Constance is the devoted mother of King Arthur. Constance was widely used in the seventeenth century by Puritans: Constance Hopkins was a young passenger on the Mayflower.
 The fictional Constance Billard School appears in TV's Gossip Girl, and Constance was the first name of the decidedly non-prim and proper Lady Chatterley.
 Oscar Wilde's wife was Constance, and Mozart's spouse was the German form Constanze, nicknamed Stanzi.
 Though Constance has been neglected here for a number of years, it's still ranks at Number 120 in France.
 Trivia tidbit: Constance was the birth name of 1940's peekaboo-hairdo star Veronica Lake and also, not surprisingly, Connie Britton.

Constance

This name for the sweetbriar shrub is a bit too reminiscent of eggplant. 

Eglantine

Eulalie hasn't ranked in the US Top 1000 since 1899, but its French roots might make it more appealing to modern ears than its sister Eulalia.
 "Eulalie" is a poem by Edgar Allan Poe, and the name also appeared in Gone With the Wind and The Music Man. It has been on the French popularity list for most of the 2000s. Eulalie Spence was a playwright from the British West Indies who contributed to the Harlem Renaissance.

Eulalie

Enguerrand

Felicie

This cross-cultural name, found in Wales, Brittany, and Spain, is a surprise star in the U.S. in recent years, largely thanks to actor Gael Garcia Bernal. It's especially popular in Texas.

Gael

Ghislaine still sounds unusual to us, even though in France this name is dated. It can also be spelled Ghislain.
 
In the US, it is best known through association to Ghislaine Maxwell, the French-British socialite indicted in the Jeffrey Epstein scandal.

Ghislaine

Heloise is an ancient name related to sleek, peppy classic Eloise. Both ultimately derive from the Germanic name Helewidis, which became Helewis in medieval England. In the twelfth century, the name was borne by the beloved of the French philosopher Pierre Abelard, who was considered to be one of the most learned women of the Middle Ages.
 
Most familiar to Americans as the author of Household Hints, Heloise is ready to reclaim its fashion status.

Heloise

Hilaire, a name that has rarely been exported out of its native France, was originally bestowed in honor of the fourth century bishop and theologian St. Hilaire of Poitiers.

Hilaire

The pure, simple HONOR--as chosen by Jessica Alba, is perfect as it is. It does have some literary cred though--Henry James created a character called Honorine  for his novel The Tragic Muse.

Honorine

Hortense is actually the French feminine form of Hortensia, the name of a strong, politically active early Roman woman. Hortense began to be used in the English-speaking world in the nineteenth century. Napoleon had a stepdaughter named Hortense, it was the name of one of the main characters in the film Secrets and Lies and is also associated with novelist Hortense Calisher. As unappealing as it might be to most American parents, Hortense is now Number 155 in France (as of 2021).

Hortense

Isaure

Now that Tristan has been rediscovered, maybe it's time for his fabled lover in the Arthurian romances and Wagnerian opera, a beautiful Irish princess, to be brought back into the light as well. 
 This would make an artistic and romantic choice, as the medieval heroine is seen as a symbol of undying love. 
 In Marilyn French's novel The Women's Room, the character Isolde is nicknamed Iso. Isolde is currently a Top 500 name in the Netherlands. Variations include Iseult, Isolt, Isoud, Isolda and Yseult.

Isolde

A rare French name derived from Latin lupus "wolf". It is most often found in the compound name Jean-Loup, as in Jean-Loup Chrétien, an astronaut and the first Frenchman in space.

Loup

Pretty name that may pose pronunciation problems -- it's meer-AY -- but is well worth the effort. 

Mireille

Mahaut

Nadege

Ombeline

Pierrick

Quitterie is a quirky saint’s name which is considered très chic in France at the moment. St Quiteria was a 5th century virgin martyr who was killed after refusing to renounce her Christian faith in order to marry. 
Her name may derive from Kythere ("the red one"), a title of the Phonecian mother-goddess Astarte, perhaps via Greek Kythereia, an epithet of Aphrodite.

Quitterie

Roch

mayuu's list "Unusual French names actually used in France" of 28 great name ideas: Aglae - Roch!

Unusual French names actually used in France

All of those are well known in France, most of those are people I know !
I didn't inclure accents.