From the DOF:

California’s population dipped by 182,083 residents last year, bringing the state’s total to 39,466,855 people as of January 1, 2021, according to new population estimates and housing data released today by the California Department of Finance (May, 2021).

The press release also reports that some of the decrease was attributed to excess deaths in 2020:

The COVID-19 pandemic increased California deaths in 2020 by 51,000 
average death rate for the three preceding years. “Excess deaths” rates above the past threeyear average – were observed in 51 of the state’s 58 counties. 

But the story is a mixed bag – there is significant growth in a number of inland cities, northern and southern but certainly not limited to those areas as illustrated in the interactive graphic from Cal Matters (see Cal Matters excellent write up here).