I have added the hashtag fp4 to your OP. There have been a surprising number of similar enquiries maybe coinciding with the start of the /e/ server outage where many older builds become unavailable.
A fresh install, Install /e/OS on a Fairphone FP4 - “FP4”, may well well be the cleanest and safest approach.
If you are thinking of a dirty upgrade you need to consider how many Android versions you are going to have to jump.
You have to take into account the Different Build Types, and which you have.
I suggest you use this [HOWTO] Give complete /e/OS version info easily for support, answers, comparison etc to understand your current build.
One further thing; open your bootloader and check whether you Bootloader is locked. Be aware that unlocking the bootloader will Format data.
There are a few more success stories within the group of fp4 threads since early October.