Hello Monoecho,
Thank you for bringing this to our attention. We appreciate that you've taken the time to post your concern here in Microsoft Community Forum.We understand that you want to sync or upload a folder from your Android phone to OneDrive. Let’s check on this together and find ways to address this matter.
I am an Android user and I have replicated the issue here on my end using my personal mobile phone and yes you're right there's no way for us to upload a folder instead you can only upload files but not the entire folder. I truly understand how convenient to have this feature available in OneDrive for Android however this seems to be a feature limitation since we're using an Android device and it's not yet supported because OneDrive for Android has a certain limitations compared to a OneDrive for desktop.
As a workaround ( I have been doing this for years now) you can plug your phone onto your desktop computer and browse your folders and go to OneDrive online and upload folders from there as it will give you option to upload a folder online using a desktop computer. You can use the cable of your phone charger to connect your phone to your computer and make sure you allow your desktop to browser files and folders from your phone ( you can see the option when you plug in the phone to your computer).
We encourage you to provide feedback or suggestions with OneDrive for Android so that our support engineers can do something about it.
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Thank you for understanding and have a good day ahead!
All the best,
Juhn Jac,
Consumer M365 Forum Moderator