I'm using qBittorrent… and I know that my ratio is not good enough.
But I just saw that no torrent is uploading. I just downloaded a popular movie, which I hoped that will be seeding. But nothing happens.
I do use a VPN, but I already switched it off, but still nothing. Also the firewalls I disabled temporarily, still no upload traffic.

Is there something I must do?

Are there a lot of active downloaders for the files you are seeding and they can't connect to you or is it that no one is trying to download the files at all?

Disabling your VPN and your firewall should not be necessary and doing so is dangerous, especially for the firewall.

You have uploaded a lot overall, so has anything changed recently?

Your ratio is borderline.  It would help not to download anything that's not freeleech until you get your ratio up.