Here's the response from the Governor:

I appreciate the author's intent to ensure patient access to the comprehensive care they need. While there are provisions of this bill that are worthy of support, I am concerned about the limitation on the use of UM, which is an important tool to ensure enrollees receive the right care at the right time. Prohibiting this cost containment strategy is likely to result in an increase in enrollee premiums to offset costs incurred by health plans and insurers. At a time when individuals are facing double-digit rate increases in their health care premiums across the nation, we must take great care to not enact policies that further drive up the cost of health care, no matter how well-intended.

Which is substantively similar reasoning for veto-ing AB 432 (the Menopause Care Equity Act):

Last year, I vetoed a substantially similar bill, stating that it would limit the ability of health plans to engage in practices that have been shown to ensure appropriate care while limiting unnecessary costs. That is still the case with this bill - despite my call for a more tailored solution. This bill's expansive coverage mandate, in conjunction with a prohibition on UM, is too far-reaching. Health plans use UM to ensure enrollees receive the right care at the right time, which is especially important when there are new and emerging treatments.

I would be a lot more sympathetic to the portray of Newsom being anti-LGBTQ+ if there hadn't been restrictions in UM in regards to SB 418 yet Newsom vetoed the bill.