but in the friendly mode is it allowed to cheat?

What are „friendly matches“ after all? If there are friendly matches, then there are unfriendly matches, too, I suppose.

Matches, and social interactions in general, should always take place in a friendly manner. I agree with @Arihol and @WassimBerbar that cheating is never allowed and that it is always bad.

It really does not matter if you are playing chess with a friend or a stranger. Every being deserves respect. We are all equal. We are all beings with feelings.

I wish a lot of interesting, fun chess games and good talks with nice people to all of us. :-)
Take care.

Edit:
In addition, cheating is against the terms of service, of course:
https://lichess.org/terms-of-service

There is nothing " Friendly " ABOUT CHEATING ... EVER AT ANYTHING ... Understand ???????????????????????

@ThunderClap said in #12:

There is nothing " Friendly " ABOUT CHEATING ... EVER AT ANYTHING ... Understand ???????????????????????
Depends on if Lichess considers it "cheating" or if your friend does.

If you and a friend both agree that the engine should be allowed, why should Lichess care?

@thefrickouttaherelol said in #13:

If you and a friend both agree that the engine should be allowed, why should Lichess care?

I‘m not into programming and/or writing code myself. However, I assume that such a feature would make Lichess vulnerable to black hats and grey hats. In addition, I don‘t see the point in cheating* if it‘s not for bug hunting and thus improving the software for the Lichess community. Thus, I‘m against it.

Edit:
*But then, it would not be called „cheating for bug hunting“, but something like „bug hunting“, „stress testing“, etc.
In addition, it is already the task of the Lichess dev team and not standard users.

Again, I would like to refer to the terms of service where cheating is clearly mentioned as forbidden:
https://lichess.org/terms-of-service

I hope I was clear.
Sorry about my wall of text.

No, using an engine or otherwise cheating is not allowed - even in casual games against friends. Please note that it is forbidden even if your opponent knows it in advance. For more information refer to this page: https://lichess.org/page/fair-play.

@lavender729 said in #14:

Again, I would like to refer to the terms of service where cheating is clearly mentioned as forbidden:
lichess.org/terms-of-service

None of this answers the question of WHY though. If two players in a friendly match agree that engine use is allowed, then it's only "cheating" because Lichess says so.

Lichess has BOT accounts. https://lichess.org/blog/WvDNticAAMu_mHKP/welcome-lichess-bots

Cyborg/Centaur chess (man and machine teaming up)

thefrickouttaherelol said in #13:

If you and a friend both agree that the engine should be allowed, why should Lichess care?

We used to not care. There were several reasons for changing that. The one that is easiest to explain is the following: We rarely have a way of knowing what two players did or did not agree on.

What could be more friendly?!

@edoki said in #5:

#3 you used to have a Danish flag in your profile, but now a Russian flag?
Possibly he is with Russia amid their invasion of Ukraine!