Help! Cant install it in ChromeOS [Debian GNU/Linux 11 (bullseye)]

[Hellromana]

Hello! First of all i'm not a Linux user. I just got a Chromebook that runs ChromeOS Flex. It uses Debian GNU/Linux 11 (bullseye).
I just folllowed the steps, but at the last command I got error messages such as:

Error! DKMS tree already contains: rtl8821ce-v5.5.2_34066.20200325
You cannot add the same module/version combo more than once.
Error! Your kernel headers for kernel 5.15.89-16159-g41ce64d8a22f cannot be found.
Please install the linux-headers-5.15.89-16159-g41ce64d8a22f package,
or use the --kernelsourcedir option to tell DKMS where it's located

Am I doing something wrong? By now I'm just trying to discover how to upgrade the "kernel header" to "kernel 5.15.89-16159-g41ce64d8a22f", and I don't even know if it's possible.

Here is the log:

hellenalvesmc@penguin:~$ sudo apt-get update
Hit:1 https://deb.debian.org/debian bullseye InRelease
Hit:2 https://deb.debian.org/debian bullseye-updates InRelease
Hit:3 https://deb.debian.org/debian-security bullseye-security InRelease
Ign:4 https://storage.googleapis.com/cros-packages/111 bullseye InRelease
Hit:5 https://storage.googleapis.com/cros-packages/111 bullseye Release
Reading package lists... Done

hellenalvesmc@penguin:~$ sudo apt install git build-essential dkms
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
build-essential is already the newest version (12.9).
dkms is already the newest version (2.8.4-3).
git is already the newest version (1:2.30.2-1+deb11u1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

hellenalvesmc@penguin:~$ git clone https://github.com/tomaspinho/rtl8821ce
fatal: destination path 'rtl8821ce' already exists and is not an empty directory.

hellenalvesmc@penguin:$ cd rtl8821ce
hellenalvesmc@penguin:/rtl8821ce$ chmod +x dkms-install.sh
hellenalvesmc@penguin:~/rtl8821ce$ chmod +x dkms-remove.sh

hellenalvesmc@penguin:~/rtl8821ce$ sudo ./dkms-install.sh
About to run dkms install steps...
Error! DKMS tree already contains: rtl8821ce-v5.5.2_34066.20200325
You cannot add the same module/version combo more than once.
Error! Your kernel headers for kernel 5.15.89-16159-g41ce64d8a22f cannot be found.
Please install the linux-headers-5.15.89-16159-g41ce64d8a22f package,
or use the --kernelsourcedir option to tell DKMS where it's located
Error! Your kernel headers for kernel 5.15.89-16159-g41ce64d8a22f cannot be found.
Please install the linux-headers-5.15.89-16159-g41ce64d8a22f package,
or use the --kernelsourcedir option to tell DKMS where it's located
Finished running dkms install steps.

Regards,
Hellen.

[tomaspinho]

I think you’re missing a sudo apt-get install linux-headers to get you the missing kernel headers for your kernel version.