Garmin Support Answer:
If you have a wearable device with an optical heart rate sensor, your heart rate is determined by the sensor sending LED light signals through your skin and registering the changes in light due to blood flow through the vessels and capillaries. This measurement is based on the amount of blood flowing through the skin. The more blood, the higher the heart rate. The frequency of the measurements increases when the device detects increased movement, such as a walk or run.

So if you have a tattoo on your wrist, we do not recommend using such a sensor. The accuracy will be lacking.

Yes, I know, I found that too, that's why I'm asking... it would be best to test it, maybe it's individual depending on the tattoo.
Does that mean that if I were black now, it wouldn't work either? That would be a bad patent.

I know that the Apple Watch has (had) problems. otherwise I find statements like:

However, if you have a lot of hair on your wrist, a tattoo or a dark skin tone, the optical pulse measurement may not be very reliable.

I think it's best to contact the manufacturer's direct support team for a definitive answer.

Nope, unfortunately it doesn't work with tattoos.

I have a tattoo on my arm... where the watch sits is a spider's web with shading... so it's already quite dark and it doesn't work for me!!! even with the new active 2 from samsung... left arm nothing works... also the akways on right arm arm without problems...