The mayo clinic suggests it could be 70%, and I have seen others suggest 80%. I have not seen anyone suggest as low as 10/20% so I think that suggestion is a huge outlier and even the paper you link says as much.
There actually has been several papers posted to r/COVID19 that have suggested that the herd immunity threshold is likely overestimated. This is because vulnerability to infection isn't uniform across the population. Some people will be more likely to be infected, either due to biological reasons, like a weaker immune system, or sociological ones, like living or working in an area where transmission is far more likely. Most of the higher estimates of a herd immunity threshold of 70-80% are based on transmission dynamics from early in the pandemic, which mostly consisted of these people with higher probabilities of infection. Once this population starts to get burned out, the transmission of the virus also slows, which means that the herd immunity barrier also drops.
One of the papers hypothesized that this demonstrates why areas like NYC got hit so hard initially and have remained stable since. Seroprevalence surveys back in the early summer indicated that between 20-30% of NYC residents had contracted Covid already. The lockdowns obviously blunted the surge, but unlike other areas of the country, as NYC has opened back up, there hasn't been much of a second wave at all. With more than 2/3rds of the population still without any kind of exposure to the virus, you would expect a dense city like NYC to see a large increase. The paper concluded that this is evidence that might suggest that the herd immunity barrier is far lower than initially estimated. I've seen some papers suggest something closer to 20-50%, but nothing so low as 10%. I'll see if I can dig up some of the preprints to post here.
That's because 70/80% estimates assume that the population is entirely vulnerable, while instead it looks like it's partially vulnerable. Hence the estimates would need adjustment.
One of the papers hypothesized that this demonstrates why areas like NYC got hit so hard initially and have remained stable since. Seroprevalence surveys back in the early summer indicated that between 20-30% of NYC residents had contracted Covid already. The lockdowns obviously blunted the surge, but unlike other areas of the country, as NYC has opened back up, there hasn't been much of a second wave at all. With more than 2/3rds of the population still without any kind of exposure to the virus, you would expect a dense city like NYC to see a large increase. The paper concluded that this is evidence that might suggest that the herd immunity barrier is far lower than initially estimated. I've seen some papers suggest something closer to 20-50%, but nothing so low as 10%. I'll see if I can dig up some of the preprints to post here.