Just installed DCS on a new PC.
Btw. entering multpiplayer games takes noticeably longer now in 2.5.6 stable than in 2.5.5 stable before.
ED recommends not to simply copy DCS and run it but do kinda fresh install via the method posted in the FAQ (https://www.digitalcombatsimulator.com/en/support/faq/):
Unfortunately this method didn't work for me but what you still can do in this case:
1. On your current PC do a DCS World repair (should be in the start menu in the DCS folder).
2. The repair tool will ask you to either keep the files not belonging to DCS or to remove them. If you remove them, DCS will place them into a "_backup.xxx" folder below the "DCS World" folder, so they are not totally lost ;). Removing them will give you a cleaner DCS for the installation step.
3. Save your DCS on an external harddisk or whereever you have still space. It were almost 200 GB in my case. Can be zipped or not but you have to be able to access and unzip with your new PC.
4. On your new PC, install DCS freshly via the web installer. Let the DCS launcher run for some time so it will build the folder structure in the "_downloads" folder below "DCS World". I noticed that all the files are unpacked there and ready to just being copied.
5. Copy those folders from your original DCS into the new "_downloads" folder. Just copy those folders, no additional ones (like the _downloads, _backup.xxx and SRS folder). You can skip the files already inside there.
6. Continue the installation with the launcher. It should check for already downloaded files and just copy the files from the "_downloads" folder and only download some missing files.
Remark: the installation is usually done in two steps, first DCS World then the additional modules you purchased.
7. After the installation is complete, do a DCS repair again.
8. Delete the remaining content in your new "_downloads" folder.
This will still speed up the installation, especially if you have a slow internet connection.
9. But that's not all because all your config files are in the "...\Users\<Username>\Saved Games\DCS" folder (short: under "Saved Games" in your user folder).
You can either just dumbly copy all those files or clean it a bit (tracks, log-files, multiplayer server favorite list, ...). If just copying, take care that the path to this Saved Games\DCS is the same as before or you may have to adapt some paths in the config files.
Anyways I had to reapply all the joystick settings to every plane in the new DCS. They are usually in "...\Saved Games\DCS\Config", so this one is important.
Beware that there may be other folders in the "Saved Games" depending on your purchased modules.
10. After applying your Saved Games\DCS start DCS. Enter a multiplayer game requiring an unmodified client, this will tell you immediately if your client is ok. If not, do a DCS repair again.
Useful tools: a better text-editor, a tool to zip/unzip, large harddisks ;)
Good luck !