To use phones people need to first buy them and regularly recharge them. Homeless people already have hard time to find other necessities.
Also in some countries you don't have any option to get any sim card and use it without first registering to your name and your address.
For the safety aspect yes, it is harder to rob them of their money but the phones are very easy to steal.
Cashless is only good if you already have some base level of comfort and do not care about your financial privacy. Every cashless transaction you make is recorded, tracked and sold via however many middle man you use.
I am not saying everyone has to use cash but people should have the freedom to choose how they want to pay.
Can I ask how you set authentik up for tailscale? I tried that but got stuck with the webfinger step. I can't wrap my head around that.