The issue with Thwaites Glacier is it has a tapered edge that generally resists thawing, but that widens out to a huge contact surface area once erosion by salt water progresses.
This glacier alone will cause a global sea level rise of three feet.
[0] - https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/201...
Where did you get that information? This source from Wikipedia says it would cause a rise of 4 inches:
At the beginning of 2020, researchers from the ITGC took measurements to develop scenarios for the future of the glacier and to predict the time frame for a possible collapse: The erosion of the glacier by warmed ocean water seems to be stronger than expected. The researchers noted with concern, that at the baseline of the glacier, the temperature of the water is already more than two degrees above freezing point. They confirm thawing of the Thwaites glacier contributes about four percent of global sea-level rise. The collapse of this glacier alone would raise the sea level by about 65 centimetres (25 inches).[25]
Your quote says 4% of global sea level rise from this one glacier, not 4" - it says 25" at the end there.