Can't Delete BootCamp Partition

I’m having trouble deleting a partition from my internal hard drive. I’m using a late 2014 iMac running MacOS 10.15.6

I created a 100GB partition on my hard disk to run Windows 10 using BootCamp. I then try to install Windows 10, but the installation wasn't able to finish. After searching for how to delete it online, I opened Boot Camp Assistant and selected the “Install or Remove Windows 10 or Later Version” option and followed the steps. Next, I opened Disk Utility to verify that the process worked. I am no longer able to see the Windows 10 partition in Disk Utility, but it seems my hard disk is still partitioned. My hard disk should show a total of 500 GB of storage, but it is still only showing 400GB. As mentioned, I’m not able to see the 100GB Windows 10 partition anywhere in the Disk Utility. I call the Apple Support, but they told me that I have to format my main disk by using the Time Machine Restore (command+R). It seems that I'm not the only one in this case, I look on the different topics, but when using the terminal, I don't have the same results.

I have run Disk Utility’s first aid function in recovery mode and no issues were detected, expet when making an SOS in the Container Disk 1 (see attached picture) > " error : directory valence check : directory (oid 0xa002e) : nchildren (1) does not match drec count (0)

Does someone have any insight on how to reclaim the extra storage from this “deleted” partition?

For info, I've tried to follow the different steps in this old topic, but my configuration seems different :

https://discussions.apple.com/thread/251265010

I attached some screenshots so you can have an overview of the problem

thanks a lot for your help,

Teddy