Frieren is not an Isekai though.
Without having seen this: Most Isekai are purely power trip wish fulfillment and they are diametrically opposed to having stakes, yet act like there are stakes. This makes them terrible. Don't make the protagonist OP, or make the protagonists OPness so over the top it becomes funny and the Isekai can be good. There, I fixed it.
Also: don't do slavery.
Also: don't do slavery.
if you're gonna do slavery, kill the slavers and free the slaves
John Brown isekai
https://www.royalroad.com/fiction/57505/his-soul-is-marching-on-to-another-world-or-the
Fair, but I don't trust these authors to do that right so they best just don't do it.
My main problem with Isekai is not that MC might be OP, but rather that their character is nothing unique. You always have this stupid "Ah, you are already mature with 15!" line, which is a bad excuse for sexualising someone who is underage. And then you have always a harem, because it is common to marry 93483929248432 women! MC is of couse stupid as fuck and never get it if a girl is intereated into him (its of course male). Everytime the same shit over and over again.
I found a YouTube link in your post. Here are links to the same video on alternative frontends that protect your privacy:
