The LED vs. OLED thing is very much a matter of taste. Most people these days worship OLED because it offers perfect blacks
by controlling the brightness of each pixel separately. LED doesn’t have such accuracy and can never achieve perfect blacks. You can (and must) use “local dimming” to achieve better blacks on LED, but the dimming zones are limited and sometimes you can see brightness “bleeding” to dark areas. But anyway, if you get a LED TV, it is VERY important you get one that has local dimming function as the cheap TVs don’t have it.
However, that doesn’t mean OLEDs are perfect. The OLED technology causes heavier stutter
to the image than LED. You can only combat this by turning on the “image smoothing” aka soap opera mode, which will add artificial frames to make motion stutter less. As a result, even mega budget movies begin to look like cheap home videos, and Akira Kurosawa films begin to look like they were shot digitally by your neighbour (they loose the “cinematic” look of 24fps and gain a news “video” kinda look). Most professional reviewers these days don’t even mention about this because they are so used to motion smoothing.
I should mention even LED TVs these days have notable stutter, but less than OLED. I don’t have much experience of OLED personally, but I did watch Assault on Prescient 13 at a friend’s place last summer on his LG and it stuttered like hell. So personally I’m avoiding OLEDs at all cost.
The “filmmaker mode”
you mentioned is basically a preset that turns off most of the TV’s image enhancement features. Note that almost all “image enhancement” features actually make the image worse (e.g. remove grain by making the image soft, smoothen the motion with soap opera mode etc.). So it’s not a gimmick, although you can also achieve pretty much the same result if you just disable all that crap manually.
Speaking of which, unless you want to pay for calibration, I recommend buying a TV that already looks good with factory settings. The calibration thing is partly a marketing fraud as there are huge differences between TVs. Some TVs look like crap with factory settings and require heavy (probably professional) calibration. Others, like many higher end Sony TVs, look very good out of the box
and only require you to do basic adjustment (e.g. choose “cinema mode” as starting point, disable motion smoothing and grain removal, lower the brightness, use “expert” colour profile) and you will get a solid image. Of course, to get the absolute best out of the TV professional calibration is needed. But the question is, a) do you consider it worth the money, and b) can you actually tell the difference.
Now, I recommend using the website Rtings
as starting point when deciding what TV to buy. They have tons of TV reviews and they also score things such stutter, local dimming, and image quality before and after calibration. They also have recommended setting for each TV. Be warned though, they are OLED fans. Nowadays you can only read 3 reviews for free per month, but you can bypass this limit with VPN.
(oh and note that model numbers / names often differ between countries. Like my Sony 950H is 95H in UK and 9500H in Japan. But with a little research you should be able to find the corresponding model)