i know this is really stupid and makes no sense canon-wise but what if it was 202k, and the kira task force had a discord server, and that was where they communicated miscellaneous things like, "@/mtsudg could you stop by a coffee shop and buy us some food? what does @/everyone want"
obviously no important info goes through the server, it was simply easier to have a place where they could communicate without including their personal identities.
now imagine, discord checkpoint had released recently, right? the kira task force does not care about these. after all, they only had the app strictly for work reasons. misa however, does. the first thing she does on her 'date' with light is to show him her checkpoint.
when she looks over at L, he shows her that his sidekick is, strangely, light. which makes no sense, because they're literally together 24/7. why would her light be his sidekick? light is literally her sidekick!!! (but light is never lesser than misa! they're equals of course!) ryuzaki are you on that side of the fence?
misa is very excited to see light's checkpoint, wanting to win against ryuzaki. light is hers clearly!!! and light, being very uninterested in their social lives during a murder investigation, just shows misa his checkpoint without much thought.
L and Misa both lean in, one steaming with excitement and the other curious yet certain.
Misa thinks, I'll be Light's sidekick!
L thinks, Considering that Light-kun and I sometimes talk with this application, it is possible that I could be his sidekick.
Lo and behold, it's Matsuda.
Matsuda is the person Light messages the most and it baffles everyone. Even Matsuda, because he didn't realize he sent Light so much dumb internet videos during work hours and Light replies a lot to them.
Misa is dumbfounded. She can't accept this! L has his thumb pressing on the bottom of his lips, thinking as always. Light does not know what's going on inside his head.
The very next day, L had decided that they would use a different place to communicate now. The checkpoint meant their data was being collected-- which is obviously a bad thing!!!