"An unauthorized access error occured when trying to write to disk" Error

You could follow a guide like this;
 
https://support.klei.com/hc/en-us/articles/360036947812-Oxygen-Not-Included-is-crashing-at-or-just-after-the-Klei-Logo 

But before doing stuff that might mess something up, check your anti-virus.
If it has a ransomware shield, it could be blocking the components of ONI in steam under your 'program files' from accessing the components in 'my documents' as it may see it as a malicious action.
Try Exempting the paths to both locations and allow the apps if your anti-virus has that function.
Hope that helps.

Happy Holidays.

Edit; I just realized, it's funny how this tickets problem and another ticket were posted on the same day
 

No idea if their related, but it does make one wonder.

Edited December 24, 2020 by ChainedDjinn
Noticed something is all, an observation.

On 12/25/2020 at 12:59 AM, ChainedDjinn said:

You could follow a guide like this;
 
https://support.klei.com/hc/en-us/articles/360036947812-Oxygen-Not-Included-is-crashing-at-or-just-after-the-Klei-Logo 

But before doing stuff that might mess something up, check your anti-virus.
If it has a ransomware shield, it could be blocking the components of ONI in steam under your 'program files' from accessing the components in 'my documents' as it may see it as a malicious action.
Try Exempting the paths to both locations and allow the apps if your anti-virus has that function.
Hope that helps.

Happy Holidays.

Edit; I just realized, it's funny how this tickets problem and another ticket were posted on the same day
 

No idea if their related, but it does make one wonder.

Thanks for the suggestion but I've already tried everything listed there (for once it isn't my antivirus over reacting cause it was disabled this time).

On 12/24/2020 at 11:59 PM, ChainedDjinn said:

its still can't fix ? 

 

Go to Windows Security -> Virus & threat protection -> Ransomware protection -> Manage ransomware protection -> Block history

 

you should see a branch of "Protected folder access blocked" item, click to expand. Find the one saying:

App or process blocked: OxygenNotIncluded.exe

Protected folder: %userprofile%\Documents\Klei\OxygenNotIncluded\

 

On the right bottom corner, there should be a "Action" drop down, click "Allow on device"

(The screenshot below doesn't have the "Action" dropdown, because I already allowed it)

Edited May 6, 2021 by Polyamide
clearify

The above post by Polyamide WORKED for me. Thanks man