Is your phone running a GNU distro or rooted Android, or is it just regular Android with a Termux chroot?

No problem, I love when people show curiosity, and I’m happy to help where I can

(Why are there % signs)

Good question, here’s the explanation man sudoers offers:

The definitions of what constitutes a valid alias member follow.

       User_List ::= User |
                     User ',' User_List

       User ::= '!'* user name |
                '!'* #user-ID |
                '!'* %group |
                '!'* %#group-ID |
                '!'* +netgroup |
                '!'* %:nonunix_group |
                '!'* %:#nonunix_gid |
                '!'* User_Alias

       A User_List is made up of one or more user names, user-IDs
       (prefixed with ‘#’), system group names and IDs (prefixed with ‘%’
       and ‘%#’ respectively), netgroups (prefixed with ‘+’), non-Unix
       group names and IDs (prefixed with ‘%:’ and ‘%:#’ respectively),
       and User_Aliases. Each list item may be prefixed with zero or more
       ‘!’ operators.  An odd number of ‘!’ operators negate the value of
       the item; an even number just cancel each other out.  User
       netgroups are matched using the user and domain members only; the
       host member is not used when matching.

TL;DR % lets the system know the following word is a group name, instead of a username

Y’all seriously overestimate thr average user:

Debian. It’s simple, stable, minimal upkeep, rarely if ever has breaking changes, and all this out of the box.

Someone new doesn’t need to be thrown in the deep end for their first foray into linux, they want an experience like windows or mac: simple interface, stable system, some potential for getting their hands dirty but not too much to worry about breaking