Celestial Harbor can be considered the first online SRT, hosted all the way back in 2018.

A summary of the event described by Daikyi, the organizer:

Celestial Harbor is the first ITG Mods SRT to be held at a venue, as well as online at the same time. This means that people across the globe will be able to experience brand new files from the comfort of their own home and keyboard/pad. With online score submission and login features being freshly implemented for this event, this will hopefully serve as a proof-of-concept event to really show that having an online SRT is possible, opening up the doors to a world of possibilities for future prospective SRT writers.

The following footage is from a decompiled build, modified to run offline on an existing NITG 4.9 install.

All songs featured on this tournament are available to download on the NotITG website's SRT Lore pack.