No single city needs to supplant the San Francisco Bay Area as a high-technology center in order for that area to lose its dominant position. An unofficial confederation of other locations, ranging from urban to rural, could each sap resources from the centralized Bay Area talent.
A slow bleed from many cuts.
No single other location needs to rise in order to overthrow mantle. This is exemplified by the chart below; while there has been an increase as a result of the COVID-19 events, there was a pre-existing upward trend that appears to be continuing following the spike.