Why can't I move a file from the Downloads folder immediately after downloading?

Very small picture is painted.

Part 1 of 3

1 - Restart in Safe Mode. This will perform a Disk Repair, clear cache files and only load Apple Software, extensions and fonts. The boot up will be slow and can take some time - Normal.

2 - Safe Mode will also eliminate Third Party Software, extensions and drivers from loading 

3 - Does the issue present in this mode ?

4 - Sometimes a Safe Boot followed by a Normal Boot will just put things right.

5 - If not - there could be something in the main User Account playing up. To further isolate this - Set up users, guests, and groups on Mac. Then log out of the Main User account and log into the dummy account and test again if the issue persists.

6 - If the issue is present in the dummy account - then, this appears to be a System Wide issue on the computer.

7 - Download the Application Etrecheck directly from the Developer.

This is a Diagnostic Tool that makes no changes to the computer.

It makes a coherent and readable inventory of both the Hardware and Software used on the computer 

The application is free or paid from added features. 

The Report will Not Reveal Any Personal Information. 

Post back the Full Report - copy and paste - >>>> using the Additional Text Icon ( 3rd Icon to last ) <<<<

We can have a look at the report for possible issues and may have possible suggestions to resolve the issues.

Part 2 of 3

Any Third Party Applications that will interfere with the normal operation of the OS,  is an invitation for disaster and comprise the Operating System

Certain Applications maybe available on the Apple Apps Store - this only means the Developer is prepared to pay Apple a portion on each sale. What the Application may do to the computer is up to the User to check this out before purchase

Any of the below should be removed as per Developers Instructions 

This will include CleanMyMac , This will include BitDefender , 

This will included Norton Antivirus , Sophos Av Software

Intego AntiVirus, McAfee, MacKeeper, Avast AntiVirus

Ad Guard, Webroot , ESET , Avira , Dr Cleaner Pro Plus

AVG AntiVirus   avira antivirus 

Trustee  

AntiVirus for Mac

F-Secure

Read some of the posting and arrive at your own conclusions.

The The Built in Security  is all that is required.

Part 3 of 3

Specific to CMM, MacKeeper and Dr Cleaner Pro Plus 

Some Contributors suggest restarting in Recovery Mode and choosing to Reinstall the Operating System over  the existing installation. 

This may or may not replace elements of the Entire Operating System including the Home Folder ( User Account )  and replace any corrupted or removed elements of the Operating System and make thing right.

Then there are Other Contributors ( like myself ) would suggest  from this link Use Disk Utility to erase a Mac with Apple silicon.

Thereafter to start from scratch and install all Required Application directly from the Apple Apps Store or Directly from the Developer.

If going this route - I suggest Not using Startup Assist to migrate things back as this will probably Re-Introduce the existing  issue that existed when the TM Backup was made 

3 questions.

1- What is the size of this file ?

2 - To where on this computer is the User attempting to move it to ?

3- How much Empty Space existing on this computer. This kind of dovetails in to first question