How do you make a good isekai without relying on either parody or satire?

You don't. Just write a fantasy manga.

then good isekai is impossible

Make good character, not bland self-insert MC or edgelord
Stop having OP MC with cheat skill
Stop take out the character sheet, make a live in world, not a videogame
Give MC a goal.

Give the MC a personality and a goal. Probably a motivation and method to return home too.
You could probably keep the cheat skill video game shit in, but it's going to be a handicap.
Bonus points for making the world interesting. Double bonus points if your story doesn't read like a poorly constructed tour to show off your worldbuilding.

Play it straight and don’t make your protagonist stupidly op for no reason. That’s literally all they have to do but that’s too fucking hard for the industry.

>follow this simple guideline to make a good story
>follow this simple guideline to make a bad story that sells like hot cakes
I wonder why idiots think this way. If it were that easy, it would already be well-known and followed widely. Hollywood has such retarded rules like "never end a title on a question mark", because they don't know any better. They still can't make a certain hit.

Make it a fantasy story and actually put work into the characters and plot.

bingo

Why doesn't anybody try to rip off FFTA? Marche is a BASED protagonist

Horror Comedy =/= isekai parody