I think the best would simply be to use the concept of “simplicité” or “facilité”.

Comment devrais-je assurer la stabilité du montage ?

• C’est simple, utilise une queue d’aronde !
• C’est facile, utilise une queue d’aronde !

Personally I’d find «c’est facile» just as condescending as «évident», and the latter a reasonable translation for “no-brainer”.

That said, a couple or three other suggestions:

• Start with évidemment, because it draws the listener in and says “you’ve already realised that …” rather than “it should be obvious that …”
• A bit of searching led me to «Ça coule de source» and «Ce n’est pas compliqué». The former is quite a figurative phrase, which compliments the listener; the latter is un peu dur).
• Obviously if you wish to avoid condescension, avoid beginning with «Franchement, je crois que la question ne doit pas se poser…» :o)

If your desire to express this concept with a noun would be satisfied by declaring the absence of an antonym/near antonym of that noun, maybe you could consider using that strategy, perhaps as follows:

Granted, there’s technically a gap in meaning between “not being something [e.g., a brain-teaser/twister] and actually “being the near opposite of that thing [e.g., a no-brainer], but it’s possible that the nuance caused by this very gap could actually present an opportunity to soften a bit the notion of “It’s a no-brainer” by replacing it with “It’s not a brain teaser,” …
… first in English (for I, in spite of your observation, often hear/see “no-brainer” used condescendingly in that language, too) …
… and then in French to slightly temper the condescending tone of …
… “C’est/Ça semble une evidence que …” with, for example:

Ce n’est pas un mystère {que
…}.

(usage example, possibly relevant, from Journal des débats, Volume 28, Issues 41-65 L’Assemblée, 1985 – Québec (Province), via GoogleBooks).

If, however, the nuance/gap between something “not being un mystère” and its “being une evidence” is either too great (i.e., “sorry, but that’s just not what it means”) or …
… too slight (i.e., “sorry, but it’s still too condescending”), …
… then perhaps you could consider a literal translation of “It’s not a brain-teaser/twister,” such as:

C{e n}’est pas un casse-tête [chinois].

(from Reverso-Context).
(but please note that this, too, might be seen as failing to help you reach your admirable goal of avoiding all traces of condescension [and some might even see it as being worse than the original in that respect])

(see also Cath S’s suggestion on this Word Reference thread on “a no-brainer”)

Une proposition de néologisme aux allures de calque morphologique pourrait-on dire mais entièrement français vu qu’elle représente la substantivation de la locution adverbiale sans effort (facilement) :

Un sans-effort [ Wiktionnaire fr. no-brainer,
Termium dans un contexte spécialisé (l’entente) ]

Une formalité d’une certaine manière, l’acte sans difficulté (TLFi A 2 b). Plus généralement on préfère ça va de soi et la facilité selon le contexte, tel que mentionné ailleurs… mais c’est un nom !