OK, didn't watch the video. Now it's clear to me.
190 CFM is 322 m3/hour, after
https://www.engineering.com/calculators/air-flow-conversion-calculator/ So it looks more than plenty to me, as long as it's not a fake spec and you get rid of any bending/restriction causing static pressure increases. 500 CFM really looks overkill to me.
I think the easiest thing would be to place duct mouth directly over your work. That way fumes would naturally go towards the duct, away from you, and your fan would need just reinforce that natural path. Having duct mouth so near your work wouldn't be needed. Deviating the fumes from natural path will require more energy. Cook rooms have the exhaust system placed over the fires for a good reason.
Just one 12 VDC, 30 CFM centrifugal fan placed in the vertical/horizontal transition would allow for a full, good-performing, no-radius at all, 90º bend without any losses whatsoever. Something like this:
https://www.digikey.com/en/products/detail/delta-electronics/BUB0812HN-00/21556245, but bigger than that. I just did a quick digikey search. I'm sure you could find one of these sized to your needs. I really think you shouldn't need much more than that. If you can't do it with a 30 CFM fan, then I would bet the ducting is the culprit, not the fan.
I wouldn't be looking for any growing tent fan, those are purchased by stoners that usually lack any knowledge of the matter and even if they have a very high IQ, they are always high and are easily fooled. Growshop salesmen are not much better. Please note that, unlike online growshops, digikey specs give you CFM, static pressure, noise, etc, right off the bat.
That trumpet-shaped black mouth looks really good to me. That shape performs much better than just a naked duct end.
In case you want to go ahead with any stoner fan, please bear in mind that even one 90º bend will cause decreased performance. One bend with a good radius is deemed to be acceptable. Any tight bend is a no-no-no. Be generous when allowing for bend radiuses. The bigger the radius, the better. One foot radius isn't really that much. Putting curved fins into the bend is said to help. There is plenty of documentation on Internet, I had some links somewhere but not in english. Also you should be exhausting on a space wider than 4 inches. Window should be open enough to allow for exhaustion without restrictions.
You could easily build your own rectangular duct with some thin MDF board, it can be cut with just an utility knife and glued with silicone. Easy to curve. It has the advantage to be rigid so it's easier to put it in place. You could tie it to, say, some cupboard when you are going to do some soldering. Rectangular duct works better, not in allowing for more CFM than the fan is able to do, but for less static pressure. It would be smooth, and could have fins easily done into the bends if deemed necessary.
You can look for pressure difference by using some length of transparent flexible plastic tubing and some water. IIRC, you place one end of that tube into the low side of the duct and bend it into a U shape. Second end into the room. Fill it partially with water/antifreeze. Then turn the fan on. The difference in pressure will make the water to climb towards the duct and this can be measured with just a scale. This is where measuring static pressure in inches of water comes from. Using antifreeze it will be easier to see it. I never did need to go that far, however.
Also I think you could place a same-size three-wire DC fan into a circular duct and measure RPM, it would at least show relative improvements. Not so easy to do with rectangular duct however.
Conclusion: I would make a rectangular duct from thin MDF board, tied to the cupboard and long enough to reach just over the soldering place. I would place a 12 VDC centrifugal fan there. I would use that flexible ducting vertically, under fan intake, and straight over the soldering place. It would have that trumpet-shaped mouth at the end. It will hang to a height where the fumes not only are exhausted but never get into your lungs, and it will quite probably be high enough not to bother you while working. I would take care how the fumes go out the window. If more bends would be needed to reach the window opening, I would place another fan in each one. That way I could carry a quite small, unobtrusive ducting that would work fine. It could be put in place and removed easily and quick. I would put something in window aperture to make sure air streams don't carry the fumes again into the room.
That worked for me when 3D printing ABS, and I was using an (really oversized) activated carbon filter, so I can't see why it wouldn't work for you with no filters at all.
Good luck.