Some of the very obvious differences between pure historic slavery and what we have now is that human rights are significantly better across the board and individuals have some degree of autonomy to decide what aspects of their self and time to sell and whom to vs previous time periods where those things were just taken from individuals.
So long as we're able to give labor that degree of autonomy (e.g. autonomy enabled by the ability to provide necessities for themselves and their family like basic food, housing, and so on) then I think we have a reasonable compromise. Vast wealth disparity (leading to monopolistic behavior on the employment side), lack of competing opportunities to sell your time/skills, and markets trending and stabilizing to states that are not labor-friendly undermine this.
This continuously peels away the abstractions we have to create autonomy for individuals and moves the needle back towards owning people like slaves, holding them on a leash indirectly through monetary mediums of exchange (i.e. currency) and so on. If I need money and food and shelter and the only real viable route to attain this reasonably is to sell myself or allow myself to be sold on abusive markets that may want more than say just my maid services (perhaps 'maids with benefits' situations, i.e. disguised prostitution) then that's what's ultimately going to happen.
We may claim the people have autonomy but we've just created complex systems around their autonomy that give the appearance of choice. People need viable and reasonable choices, not just a set of options where only one is reasonable for a stable and happy life unless we want to slowly erode back to systems like indentured servitude and beyond.
The article explicitly calls out Filipino maids as the highest selling and having been to the Philippines and now being part of Filipino family, I understand why. The country is very poor overall and the culture exports labor to import wealth due to the lack of local opportunity. Sure they can study anything and go anywhere in the world but it turns out, many go to certain middle eastern countries and pursue maid careers because it's their only real viable option. Some of the more lucky Filipinos study in school and are able to get degrees in healthcare or hotel services and work abroad in countries with better protections. Even then, they're held on a leash and abused through visa programs like in the US where they're paid a fraction of the rates their US native counterparts earn and lack mobility to transition positions readily to negotiate competitive wages, so they lose rights to employers and work in undesirable locations, under market rates, and often the under the worst sort of contract situations.
It's not like this story of maids in Saudi Arabia where conditions are even worse but it shows how we need to maintain autonomy for everyone. Aside from the being most humane thing to do, out of sheer self-interest, if you sell your labor for time in any fashion, these infringements on rights slowly peel away your rights as well. You may not see it in your lifetime but we should push for better labor rights across the globe to prevent stepping back to past atrocities we've seen in slavery systems.