Hi!
I was getting a bit impatient and I have seen a tutorial to update via Odin.
I've found a build that could be sideloaded on my phone.
All went well and I'm now with One UI 6 with all my apps and no data loss.
There is a tuto here, it's for s23 but works same way for S21 devices
Also a video on how to flash the software. It's an old video but it's the same way for one ui 6
You just need to make sure you get the right build number for your phone and region.
I have an S21 + 256gb unlocked in UK.
Don't forget the step at the end of the video to clean the cache, this is important to get a smooth experience.
I am not responsible for any damage or issue you may encounter if you follow this steps. This is just as an information and you are responsible if you want to go ahead or not. Only do it if you know what you are doing and feel confident to do so.