JDownloader 2 no longer copies my video links

I'm happy for you :)
Remember to mark the topic as resolved: https://www.commentcamarche.net/infos/25917-marquer-un-fil-de-discussion-comme-etant-resolu/

Legal... legal... um hum ;-)

• Terms of Use of Arte: https://www.arte.tv/sites/corporate/conditions-generales-dutilisation-cgu/

Among other things, you can find this...
ARTICLE 3 – USE OF THE SITES:
"The User is therefore prohibited, under penalty of civil and/or criminal sanctions, from representing or having represented, reproducing or having reproduced, adapting, modifying, transferring, commercializing, distributing or imitating all or part of the Sites or the Content."

• Terms of Use of YouTube: https://www.youtube.com/static?template=terms&hl=en&gl=FR

You can also find this...
Permissions and restrictions:
The following restrictions apply to your use of the Service. You are not permitted to:
1) access, reproduce, download, distribute, transmit, broadcast, display, sell, license, alter, modify or otherwise use all or part of the Service or Content except: (a) as explicitly permitted by the Service; (b) with the prior written permission of YouTube and, if applicable, the rights holders; or (c) in accordance with applicable law;

In short, what is allowed is online viewing (streaming), everything else is prohibited except for exceptions!
After all, everyone does what they want ;)

I'm not an "IT pro" either...
RevoUninstaller is used to uninstall software cleanly, with targeted cleaning in the registry as well.
Uninstallation through the control panel doesn't do that, -)

CCleaner also allows for cleaning the registry, but its use is now controversial for some, see the Malekal site: https://www.malekal.com/avez-vraiment-besoin-ccleaner/

Have a good evening.

Try clicking on the small gear icon at the top right that is used for column settings:

Since JDownloader is customizable, you can arrange the download window to your liking.
I saw that you can also reset the columns as if it were the first time you installed the software, if you want.