How does one analyse openings judged dubious by engines? I have recently picked up the Norwegian Defense (also known as Northsea Defense), 1. e4 g6 2. d4 Nf6.
All modern engines claim it is not good. But I have great results (14W-1D-5L in 15+10 on 2000 Lichess rating) with it and I am seriously considering adding it to my repertoire, so I would like to do some preparation work, look for critical positions where I would have to know an exact move or a plan to justify my opening.
First I have looked at games in the Lichess database. I was very surprised by Black scores in some of the variations. For example
[fen &quot;&quot;]
1. e4 g6 2. d4 Nf6 3. Nc3 d5 4. e5 Ne4 5. Nxe4 dxe4

scores 55% for Black in 2000+ rapid and classical on Lichess.
I have also looked at the Master database.
I have noted that the character of the game is mainly set within 5 moves by White and gathered some common resulting positions. From there I wanted to work further, so I looked at master games more indepth.
Some are clearly surprised by the opening and choose a timid way to play and Black equalises before move 10. In the more critical tries White keeps the advantage for several more moves, but then lets it go or even slips into a disadvantage. Also, the games where both sides offer resistance are very rare. Very often on move 7 there are 2-4 games.
Following engine lines and picking up moves that were missed is rarely helpful, as the engine of course will mercilessly squeeze the position with inhuman precision and will disarm any initiative without effort, making any active attempts seem futile. Sometimes I do not see why White is better, so I follow the line into endgames that are slightly better, but probably considered equal at sub-master level.
Of course I analyse my own games, but the opponents crumble surprisingly fast once on their own, so the opening does not really get tested much in my own games.
So, how would one proceed to prepare in unorthodox openings apart from learning by his own games?
Forget the engines. We are humans (hopefully) and are only interested in how human's play.
The King's Indian Defence (KID), a favorite opening of Tal, Fischer and Kasparov (and now played by Nakamura), has a reputation of being unsound by the engines (some positions are +1 and even +1.5) however for white playing precisely is very difficult.
For instance, the Mar del Plata Variation
[fen &quot;&quot;]
1. d4 Nf6 2. c4 g6 3. Nc3 Bg7 4. e4 d6 5. Nf3 O-O 6. Be2 e5 7. O-O Nc6 8. d5 Ne7

Stockfish evaluates it to be +1 at a depth of 40.
Simple advice for practical play is to ignore the engine evaluation and focus on the fundamentals in the opening (in the order):

Exert pressure over the center (either classical or hyper-modern way)
Develop minor pieces
King safety
Connect the rooks while developing the queen

Needless to say always look out for short tactics as you follow the above and also try to have all your pieces coordinated.