Hello c_luc9,
thank you for your reply, I found the very same article yesterday and tried out a few things it mentions, and ordered a few cables.
Happy to say that I've found a branded Thunderbolt 3 - DisplayPort lead that does the trick, the flickering and the stripes are gone.
The important bit in the product description when ordering is this: 4K@144Hz/120Hz 5K@60Hz 2K@240Hz Thunderbolt 3 to DisplayPort HBR3 32.4Gbps Type C DP 1.4 for M1 MacBook Pro 2021 Mac Mini Dell XPS 2M/6.6Ft VESA Certified
So it does matter what cable you're using. I tried a high speed 8K HDMI cable as well, but to no avail.
Kind regards,
Pal