Could it be a plugin/extension in 2018 causing the issue, that is not in 2020?

I would recommend using 2021 if possible. There has been a lot of 'under the hood' improvements with bug fixes etc.

Hi

The first thing I would check is your Antialiasing settings - if they are high enough to smooth those jagged edges and try different filters.

If that doesn't help it might be some issue with color clamping - I would try to turn on/off "Subpixel clamp" option and play with it's value. Also color clamping in Frame Buffer can sometimes give such an effect.

In the V-Ray Asset Editor...

Do you have SunLight Enabled?

Or Do you have a V-Ray Omni Light Enabled instead?

You might need to disable the omni light and re-enable SunLight.