I had the same Issue on Ubuntu 20.04 as well. There are some reasons that end up to this problem. My system is dual boot (Windows 10 & Ubuntu 20.04). And whenever i have an incomplete windows shutdown, this problem Happens.
I've seen some Answers that suggested Disabling Fast Startup in Windows 10 but haven't tried it yet. this might solve your problem too.
Here is what i did directly from Ubuntu:
Open Terminal and type the command: sudo lsblk
and at the end of the list you'll see Your Disk List known as SDA(If it's HHD). Find the drive you have problem with.(For me it was sda6). You'll see the drive name by their volume column in the list.
Hint: You can also open Files and select Other Locations in the left column to see the Drives List and their name. (at the right of their name and volume).
2.In Terminal type the command: sudo ntfsfix /dev/sdxX
and before hitting the ENTER, change the end xX to the Selected Drive Name. (in my case it was sda6 so the command would be sudo ntfsfix /dev/sda6
).
This was the only way that fixed my problem. Hope it works for you too.
NOTE: this way works for HHD dirves and SSD Drives might have a different approach or set of commands. If you have a SSD, use this method AT YOUR OWN RISK