The issue here is proprietary software being proprietary (SD801 firmware). It sucks that the SD801 went unsupported so quickly. Could Fairphone have known that beforehand? I don’t think so. They even went for a high-end SD in the 800 series. In the thread here Fairphone 3 specification speculation & leaks it seems the FP3 is going to likely have a (more common) 600 series SoC. But I am not sure how we can know beforehand how long Qualcomm is going to support that.
As an alternative to FPOS/Fairphone Open, you can install LineageOS 16 which is based on Android Pie 9. This gets new builds (including bugfixes) approx every week. However that could also introduce new regressions and bugs, as it is a rolling release.