Yeah. Had this also sometimes (in rare occasions). Before copying a virusscanner may look inside that file first it seems. I can transfer many Gb without any problems. So it seems odd. It's like something is inspecting it's content first. That may explain the delay. As experiment shutdown any external virusscanner and defender. Try again. If it goes much faster maybe this could be an explanation. No matter which extension a file has; the virusscanner looks inside each file movement or startup for viruses, trojans etc.
Other explanation; there maybe some conflicts laying behind that all. Run Start - Device Management to see if there are yellow exclamation marks visible. Run also msinfo32 to see if there are conflicts under conflicts/sharing. Normally you should see only shared IRQ's and Memory addresses because they are closely related to each other. If there is a conflict it will say so.
If you want to move files fast without the use of file explorer (and skip the ETA part); use robocopy (what user
@abactuon also pointed out) Still the most fast and reliable copy/move/etc. You can even make a script that move, copy, backup files. I made a script that copy's all OneDrive's data to a save location once a week. Scheduled this task and I don't have to worry about missing things. It's capable of verifying and mirror files. Mirroring: In that cases it only copy files that are changed so you don't have to copy each file all the time. A powerful command. It will also gives you an extensive report how it did the last time. Depending on the data size of the whole copy will be very quick and it transfers only files that are changed. It's only takes a the first time the longest time once. If there are a few changes it will finish within a second. The big advantage I find of this command; It don't calculate things first to give you some ETA. Nope. It start immediately without any fuzz. Great if you want to move or copy a complete directory from one location to an other. This command was there with every Windows version in the past and it is still here today with Windows 11 (or 12).... Just make a .cmd file once. Make a shortcut on the desktop to it (run as admin if it's needed) Doubleclick on the shortcut and it runs.... (Make sure it's piping (">") it's output to a logfile where you can see if everything went OK for later inspection.) Just open a CMD box as admin; run robocopy /? and it shows it's capability's. The possibility's are far above of what a simple file explorer can do. (you can even exclude files according on some criteria)
This is just an copy/purge/mirror example what you can do within a CMD file;
Set SDir="<Drive>:\<Path Source Dir>"
Set DDir="<Drive>:\<Path Destination Dir>"
Set LDir="<Drive>:\<Path Log Dir>"
Robocopy %SDir% %DDir% /S /E /COPYALL /PURGE /MIR /XA:SH /R:0 /W:0 /XJD /XD > %LDir%\<Filename>.log
(Note xDir: " if paths has spaces inside their name. /PURGE means if the file in the source dir is gone, than delete if it exists in the destination dir. Robocopy "lives" inside the C:\Windows\System32 dir.)
