Update June 16, 2019 2:44pm MST

It was revealed it’s a “WLED” screen not an “OLED” screen we are interested in. Hope can be found in this Linux Kernel Proposed Update message:

qcom: spmi-wled: Support for QCOM wled driver

From: Kiran Gunda

To: bjorn.andersson-AT-linaro.org, linux-arm-msm-AT-vger.kernel.org

Subject: [PATCH V1 0/4] qcom: spmi-wled: Support for QCOM wled driver

Date: Thu, 16 Nov 2017 17:48:33 +0530

Message-ID: 1510834717-21765-1-git-send-email-kgunda@codeaurora.org

Cc: linux-kernel-AT-vger.kernel.org, linux-arm-msm-owner-AT-vger.kernel.org, Kiran Gunda

Archive-link: Article

WLED driver provides the interface to the display driver to adjust the
brightness of the display backlight. This driver exposes two APIs to
set and get the brightness of the display backlight through the
backlight framework. This driver has the support to handle the OVP
(over voltage protection) and the SC (short circuit protection)
interrupts. It also has the auto calibration algorithm support to
configure the right strings if the user specified string configuration
is in-correct.

Kiran Gunda (4):  
  qcom: spmi-wled: Add support for qcom wled driver  
  qcom: spmi-wled: Add support for short circuit handling  
  qcom: spmi-wled: Add support for OVP interrupt handling  
  qcom: spmi-wled: Add auto-calibration logic support  

 .../bindings/leds/backlight/qcom-spmi-wled.txt     | 118 +++  
 drivers/video/backlight/Kconfig                    |   9 +  
 drivers/video/backlight/Makefile                   |   1 +  
 drivers/video/backlight/qcom-spmi-wled.c           | 999 +++++++++++++++++++++  
 4 files changed, 1127 insertions(+)  
 create mode 100644 Documentation/devicetree/bindings/leds/backlight/qcom-spmi-wled.txt  
 create mode 100644 drivers/video/backlight/qcom-spmi-wled.c  

– The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project

Original Answer

Although not an answer hoped for this Arch Linux article states:

It may be helpful to know that OLED displays by their nature do not
have backlight.

The only solution therefor is to use something like this:

$ xrandr --output eDP1 --brightness .5

• where .5 is 50% brightness, .63 would be 63% brightness, etc.