Thanks for the bootstrap link!
I just realised that I need to update the wallet to v1.9.9 too. :-)
Question, what is the next step, once I have downloaded the bootstrap.
-> Where/In which directory I need to copy into the file?
Do I need eventually rename the file bootstrap.dat into "blk0001.dat" and delete the existing one with this filename?
Folder should look something like above. If you click on "Settings--> Show autobackups" in the wallet it'll take you to the directory. Just click bank to the "syndicate" section, and drop the boostrap in there. It will be faster, but it will still take a while so just let it download, and you'll be good to go soon. You shouldn't have to do any renaming.. you should be able to just drop it in and restart the wallet. I actually used this zipfile though that I was given in discord. Not sure if it's the same.