My FP2 has done one freeze too much (actually, it only began after I installed the last FPOOS version long ago, very sad) - I’m looking for an FP4 now.
On the Fairphone website, I read “5 years warranty” and “extended support until 2028”, while Murena offers e/OS/ FP4 (that’s what I’m looking at) with only 3 years warranty (from beginning of 2024 on).
Are there any indications when FP4 will go out of production, i.e. from when it may became difficult to get replacements?
I would not rule out that the information you quote is outdated on the Murena website (they might just not have followed suit when Fairphone extended their dates). If buying from Murena is an option for you, I’d suggest you contact Murena to point out the difference.
No, we can only estimate. I would estimate that you won’t have problems to find replacements until 2028+
Afterwards, i estimate, the modules will one by one slowly fade out, but Fairphone will still have some to do repairs.
For the FP3 two modules are out, all the others are still available.
As they offer warranty for five years, even for phones purchased as late 2025, I guess spare parts will be available at least till 2030. There has been a comment on that when refurbished FP4 was on offer, but unfortunately I don’t remember exactly the phrasing.
Actually for me it reads a bit confusing.
One may purchase a FP4 with 5-year warranty but “We are aiming for software support until 2026 and may extend that to 2028.”
Hm, so I guess it’s to be read more in detail what’s included in those “5-year warranty”. Only software support, software and hardware?? 
I can only re-share what I have written on warranty elsewhere (in the thread on FP5). I think the warranty is clearly only on hardware