There are certainly many situations where regulations, licence conditions or similar mandate provision of single sex facilities. In those situations, they are legally required. However, this conversation was triggered by a question about how the Supreme Court ruling affects situations where there is no legal requirement for single sex facilities. Some posters were arguing that they are now always compulsory. That is clearly wrong.
As the Supreme Court said, the first principle when interpreting legislation is that you look at the legislation and, unless otherwise indicated, you give the words their normal English meaning. The rules around provision of single sex facilities, single sex services, etc., in the Equality Act set out when it is acceptable to provide single sex services. They do not make it mandatory to provide single sex services in any of those situations. The ruling by the Supreme Court has no effect on the interpretation of those provisions. The courts therefore would not support an attempt to argue that such facilities are, in fact, mandatory despite the clear wording of the Equality Act and that failure to provide single sex services is automatically unlawful discrimination. There may be situations where, even though there is no statutory requirement, the courts would agree that single sex services/facilities are required, but there is no way they would make a blanket ruling that they are always required.
As you say, in many, possibly most, publicly accessible locations, single sex services are legally required. But this ruling by the Supreme Court makes no difference to any locations where single sex services are not legally required. It does, however, make it clear that, if you want to provide a single sex service and rely on the exemptions that allow you to do so, that must be biological sex. If you allow trans women to use your service for women, it is not a single sex service.