Here's how to Fix Steam Game unpacking.
i. There are a few things you can try if Steam is unpacking your games slowly.

Make sure you have enough free space on your hard drive. Steam needs enough free space to unpack the game files. If you don't have enough free space, Steam will unpack the files slowly or not at all.
Close any other programs that are using your hard drive. If you have other programs that are using your hard drive, Steam will have to compete for resources, which can slow down the unpacking process.
Restart your computer. Sometimes, a simple restart can fix problems with Steam unpacking games slowly.
Verify the game files. If you're still having problems, you can try verifying the game files. To do this, right-click on the game in your Steam library and select "Properties." Click on the "Local Files" tab and then click on the "Verify Integrity of Game Files" button.
Reinstall Steam. If verifying the game files doesn't work, you can try reinstalling Steam. To do this, uninstall Steam from your computer and then download and install the latest version from the Steam website.
Contact Steam support. If you've tried all of the above steps and you're still having problems, you can contact Steam support for help. They may be able to provide you with additional troubleshooting steps or help you troubleshoot the problem over the phone.

ii. The Steam depotcache is a folder on your computer where Steam stores the downloaded game files. It is located in the Steam installation folder, usually C:\Program Files (x86)\Steam\steamapps\depotcache.
The depotcache is used to store the game files so that they can be quickly accessed when you launch a game. It also helps to reduce the amount of time it takes to download new game updates.
The depotcache can be a large folder, especially if you have a lot of games installed. If you are running low on disk space, you can delete the depotcache folder. However, this will mean that you will have to download the game files again the next time you launch the game.
It is important to note that deleting the depotcache folder will not delete your game saves. Your game saves are stored in a separate location, usually in the Steam\userdata folder.
If you are experiencing problems with Steam, you may want to try clearing the depotcache. To do this, follow these steps:

Close Steam.
Open a File Explorer window.
Navigate to the Steam installation folder.
Delete the depotcache folder.
Restart Steam.

Clearing the depotcache may fix problems with Steam, such as slow download speeds, game crashes, and errors.

iii. SSDs are better for Steam players because they offer faster loading times and better performance. SSDs are able to read and write data much faster than traditional hard drives, which can lead to significant improvements in loading times for games. Additionally, SSDs are more durable than hard drives and are less likely to fail.
Here are some of the benefits of using an SSD for Steam:

Faster loading times: SSDs can load games much faster than traditional hard drives. This can be a major benefit for games with long loading times, such as open-world games or games with a lot of assets.
Better performance: SSDs can also improve the performance of games. This is because SSDs can access data much faster than traditional hard drives, which can lead to smoother gameplay and reduced lag.
More durable: SSDs are more durable than traditional hard drives. This is because they have no moving parts, which makes them less likely to fail.
Less noise: SSDs are also quieter than traditional hard drives. This is because they have no moving parts, which means they don't make any noise when they're working.

If you're a Steam player, I would recommend investing in an SSD. It's a great way to improve your gaming experience.

iv. There are a few known errors when moving Steam games from HDD to SSD.

Steam may not recognize the new location of the game files. This can happen if you move the files manually or use a third-party tool to move them. To fix this, you can try restarting Steam or verifying the game files.
The game may not launch after it has been moved. This can happen if the game is not compatible with the new operating system or if the game files are corrupted. To fix this, you can try reinstalling the game or updating the game drivers.
The game may run slowly after it has been moved. This can happen if the SSD is not fast enough to keep up with the demands of the game. To fix this, you can try upgrading the SSD or lowering the graphics settings in the game.

If you are experiencing any of these errors, you can try the troubleshooting steps that I mentioned earlier. If you're still having problems, you can contact Steam support for help. And you may use a tool that is designed to move Steam games. There are a number of tools available that can make the process of moving Steam games much easier.