The BCM4776 was announced on 8 Jan 2020 in GPSWorld. It is the second generation dual-frequency GNSS receivers from Broadcom.
The BCM4776 is also described in the GNSS User Technology Report 2020 / issue 3, published by EUSPA. See page 34.
There are 4 different chipsets in the BCM4776X family - BCM47768 + BCM47765 (dual-frequency) and BCM47764 + BCM47762 (single-frequency).
The GPSTest Database shows the BCM4776 in various Android phones:
I suspect a multi-band BCM4776 chipset (i.e. BCM47768 or BCM47765) are used in Apple watches with an S8 CPU:
The BCM47768 is a second generation dual-frequency GNSS chipset supporting L1 + L5. It is used in the Quectel LC29D(E) + LC29D(F) modules, detailed in the IoT&M2M Modules product brochure v6.7, and shows a 10 Hz update rate.
The Xiaomi Watch S1 uses the BCM47768, clearly shown in a Chinese teardown.
Synaptics currently produce and sell the BCM47768, but it is called the SYN47768.
The BCM47765 is a second generation dual-frequency GNSS chipset supporting L1 + L5, still showing on the Broadcom website as “Active”. It is used in the Quectel LC29D(B) module, detailed in specification and product overview documents, which shows a 10 Hz update rate.
The BCM47765 appears in several Google Pixel products, including:
Synaptics may produce and sell the BCM47765, but calling it the SYN47765.
The BCM47764 is a single-frequency GNSS chipset supporting GPS, GLONASS, BeiDou, Galileo, and QZSS.
It is used in the Apple Watch Series 7 and mentioned in a device analysis on iPhoneWired.
The BCM47764KUBG can be found on parts websites, such as italian.integrated-ic.com.
Aside from this it is rarely mentioned in Google results, possibly being specific to Apple watches?
The BCM47762 is a single-frequency GNSS chipset supporting GPS, GLONASS, BeiDou, Galileo, and QZSS.
Several watches use the BCM47762, including:
Synaptics currently produce and sell the BCM47762, but it is called the SYN47762.