Какой уровень инглиша надо иметь, чтобы понимать 90% из этого видео?

Уровня особо не требуется, т. к. нет заумных слов. Просто нужно тренированное ухо на беглую английскую речь с несильным австралийским акцентом. Здесь даже автопереводчик звука в текст неплохо справляется:
Hey, guys, it's Bella. Welcome back to my channel. I hope you're all having an incredible day. If you’re new here, welcome! It's nice to meet you! I don't know if you can tell by the lighting but it is very gloomy and stormy and rainy here in Brisbane. So, it's just the perfect moment to sit down, get cozy and talk about another mystery in my day case together quickly before we get into it. I just want to thank today's sponsor Skillshare for making this video possible. If you guys don't know what Skillshare is, it's an online learning platform that has a thousands of classes. So, there is something for everybody, every skill level too, whether you want to pick up or learn a new skill or hobby, or if there's something that you are already experienced in or interested in that you just want to learn more about, it's curated specifically for learning. So, there were no pesky ads speaking of they also have live classes as well Which I think is a really cool feature. So, you can learn where that real teachers and other members in real time. Personally, I have been really into the portrait of photography class by Jessica Kobe. I have been doing social media for six years now, and I still am so incredibly clueless and awkward when it comes to taking photos, posing fine and good lighting, find a good, good background. I would actually get into bad mirrors when I had to go and take photos because I just found it so difficult to get a good one and get everything right. It's been really interesting. I would definitely recommend it if you're into photography or taking photos of any kind and if you guys are interested in checking skill, share out the first one thousand of you guys to click the link in my description. Get a one month of free trial to Skillshare to check out any of their classes, so definitely make sure you check that out. I'll leave all the information down below in the description, and let's go ahead and get into today's case.

Да это и не быстро. Только это американский. Для понимания не так нужен уровень, как для говорения.

Intermediate

Насколько мне удалось "въехать" - эта девушка старается говорить разборчиво, заранее понимая, что эта информация может быть полезна не только американцам. В этом плане её инструкции прекрасны. Особо продвинутый уровень для понимания не нужен - если всё что она говорит написать на бумаге -- получится английский для не начинающих, но и не полностью погружённых

да есть и сложнее, где не стараются учесть иностранных подписчиков

Сотый.

Не нужно большого уровня, просто аудирование надо натаскивать.