Your vaginal microbiome exists and functions, whether you have fibroids or not. Fibroid development is primarily related to hormonal imbalances (particularly estrogen excess) and genetics. There is a school of thought that associates the “estrobiome” with female reproductive tract issues.
The idea is that when the microbiome is imbalanced (dysbiosis), it allows excess estrogen to build up in the female reproductive tract, which can lead to various diseases including fibroids. A very interesting May 2022 study discovered a correlation between alterations of the gut microbiome and people with uterine fibroids. There is much to be discovered though.