I thought I had once posted a more detailed response on this topic before. I found it here:
And from the Wikipedia article I linked:
Astronomers estimate that several interstellar objects of extrasolar origin (like ʻOumuamua) pass inside the orbit of Earth each year,[11] and that 10,000 are passing inside the orbit of Neptune on any given day.[12]
Interstellar comets occasionally pass through the inner Solar System[1] and approach with random velocities, mostly from the direction of the constellation Hercules because the Solar System is moving in that direction, called the solar apex.[13] Until the discovery of ʻOumuamua, the fact that no comet with a speed greater than the Sun’s escape velocity[14] had been observed was used to place upper limits to their density in interstellar space. A paper by Torbett indicated that the density was no more than 1013 (10 trillion) comets per cubic parsec.[15] Other analyses, of data from LINEAR, set the upper limit at 4.5×10−4/AU3, or 1012 (1 trillion) comets per cubic parsec.[2] A more recent estimate by David C. Jewitt and colleagues, following the detection of ʻOumuamua, predicts that “The steady-state population of similar, ~100 m scale interstellar objects inside the orbit of Neptune is ~1×104, each with a residence time of ~10 years.”[16]