At the 2024 Chinese CPSE show, Canon displayed a prototype camera with a 250MP sensor and a new EOS R7 camera high-sensitivity extended firmware.
I assume this is the same 250MP APS-H-size CMOS sensor Canon has been marketing/promoting for years - since 2015 (see product page):
Canon announced three new sensors, including their 250MP APS-H-size CMOS sensor
Canon develops 250MP APS-H CMOS sensor, the world’s highest pixel count for its size
Via CanonAddict