I was going to recommend the fully manual KamLan 50mm F1.1 Mark I (the original, not the later Mark II) x-mount lens. Unfortunately it is no longer out there for sale.
This is a lens many did not like, but I think it is perfect for portraiture.
It offers muted microcontrast (many would call this annoying softness), and excellent bokeh. Price was $169 but of course they are no longer available new.
Kamlan 50mm F1.1 Overview: Digital Photography Review (dpreview.com)
Test portrait. KamLan 50mm F1.1 Mark I lens at F2.
The current popular taste is for lenses that are super sharp with lots of microcontrast, but this tends to bring to the forefront skin irregularities such as facial hair and blemishes and of course blood vessels in the whites of the eyes. Maybe your subjects will like that. Most don't, I believe.
If you prefer all that clinical stuff, the KamLan 50mm F1.1 Mark II lens will do the job for you and I think it might be available for $249. It is huge and heavy compared to the Mark I, which is small and light.
Since this Mark I KamLan is a controversial lens, and not available anyway, my advice is to buy a lower cost manual lens in the 50mm range, such as the 7artisans Photoelectric 55mm f/1.4 Mark II Lens for FUJIFILM X at $126:
7artisans Photoelectric 55mm f/1.4 Mark II Lens A503B-II B&H (bhphotovideo.com)
I have one of these also, and it is excellent. It has good sharpness and good bokeh, and it is not expensive. I find it very versatile but I mostly shoot landscapes. You might like it, and if you want to find out how it feels to use a manual lens the price is right.
Still, for best portraiture, I recommend the KamLan 50mm F1.1 Mark I (the original).
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Tom Schum
"Beware of taking advice from anonymous wise men." Quote from Anon.