This is a known issue for the FP6 in the stock OS as well. It was fixed in patch https://support.fairphone.com/hc/en-us/articles/24463713641234-The-Fairphone-Gen-6-Release-Notes#01H8BN3GDA63KS0V1273J9RQYM, however the issue is still present in the LineageOS build.
I hope that it will be fixed, as it is very annoying. The issue is described in detail in DNS over TLS/IPv6 issues- Apps don't load data over Wifi