Need some advice before building a ryzentosh for christmas

I am planning on building a Ryzentosh for a christmas gift. The person mainly use Adobe Lightroom and Unity.

• Should i go with an AMD GPU or a NVIDIA GPU ?
• I read that all Adobe software doesnt work on a Ryzentosh, is this true?
• Which version of macOS should i install (high sierra, mojave or catalina). I would prefer the newest but which one has the best compatibility?
• I am building a Ryzentosh to someone who will have no idea that this is not a real Mac, is it completely unrealistic?