For OLED, they produce for themselves and resell to others. They have two fabs
https://www.oled-info.com/lg-displa...t-has-started-mass-produce-oled-tvs-guangzhouhowever it does say the fab was a joint venture, but seems that might be for financial backing and not sharing of production
"The new fab was established in a joint venture established between LG Display and Guangzhou Development District (GDD). LG Display holds a 70 percent stake in the JV."
For Sony OLED tvs they source the panels from LG Display, but Sony still develops their own in-house image processor. I'm not sure where they get their LED panels from, but I personally would not consider any of their LED TVs, only OLED. Sony's best LED tv isn't on par with the QN90a.
I'm not sure what you mean by Sony having meager built in apps (if you are referring to the past, older TV or the ones out today). And while I don't know about their LED TVs have built-in, their OLED line uses google tv which has access to the google play store and all those apps.
LG uses WebOs, Samsung uses Tizen OS, I think they have their own app stores separate from google. However I wouldn't worry about lack of apps, they'll all have access to the major ones
For lots of natural light: Samsung QN90a would be the only one I would consider for now. I'm not sure what your budget would be, but currently the 65 inch is going for $2099, I suspect they'll be around $1800 for black Friday/cyber Monday I only mention that particular model, but the 55 inch is around $1500. I'll note however that I generally recommend (if you can) getting something larger, even if its a little more than you budget for. Screen size isn't something you can upgrade later.