Loom 0.8-SNAPSHOT should not be used for Minecraft 1.16 and below because it either breaks compatibility with Java <16 or it fails to comnpile with Java <16 (I forgot which one). Loom 0.8 is essential for Minecraft 1.17 (specifically 21w19a+), but for MC <=1.16, Loom 0.7-SNAPSHOT should be used.

Do you have a source for this? I personally haven't experienced any issues using loom 0.8 on 1.16 and below (I updated RSMM to use loom 0.8 as well).

astei/lazydfu@87b88ca#commitcomment-51761705

Fixed