More than half suffer substance abuse. Accounting for the fact that many of them would deny admitting to drug use when asked, this is probably a conservative number and the percentage is much higher. Also this is an US average, and it doesn't take into consideration "drug tourism" in cities like San Francisco, Portland and Seattle where drug use is literally the main goal thanks to easy drug access, therefore the drug-related homelessness ratio in some places is much higher.
They also probably take into account both housed an unhoused homeless, with the nuance that unhoused homeless are more likely to be druggies and to refuse shelter. Therefore the percentage of homeless population we see every day in our streets (which is the subset of homeless more likely to affect our day-to-day lives) have very likely an higher percentage of drug use.
Finally, the US actually has another problem: we can't fill up the supportive housing units fast enough! New York has empty supportive housing units [1]. This suggests that the total number of vacancies might be even higher, as more units are added to the system regularly.
[0] https://www.addictioncenter.com/addiction/homelessness/
[1] https://www.theday.com/state/20230529/thousands-of-nyc-apart...