What are my options when I have got a trademark issue post-launching?

If this is the owner of the trademark : https://bookis.com/ they have one national trademark registered in Norway and one international targeting most EU country alongside USA,.
(source: official trademark DB https://www.tmdn.org/tmview)

It's a very complex question.
They registered the trademark for computer programs (class 42) which is standard when you operate through websites and apps. So they can argue that you are using and reproducing their trademark for similar services (apps, etc). Still, it's not the same trademark as they registered the full orange logo and not just the word Bookis, so I think it would not be considered as identical but only similar. Infringement would then require likelihood of confusion.
It also seems that they are not using it outside of Norway (but i just had a quick look, so I may be wrong). And in USA for example with no proof of use it's hard to enforce your trademark rights.

You could try to negotiate a coexistence agreement arguing that they don't really use it outside Norway (with only Norwegian language), that there is no likelihood of confusion (because different logos, different customer targets), that you commit in the agreement to never use it to sells book and ebooks, etc etc.
That could work especially if you talk to them honestly. After all they are just people like anybody else.
Also, bear in mind that trademark owners needs to enforce their rights to avoid losing their trademarks (it's called trademark degeneration). So they may still be willing to negotiate even if they send cease and desist letters.

Source: I was an intellectual property lawyer before switching careers, but I am a little bit rusty so don't take this as an official advice. You should definitely seek the advice of a lawyer!