I think there are various efforts to produce some guidance on the topic. The most recent one I saw was this one, which is a pretty good review and highlights for example the need to adjust for baseline covariates. The one part I really disagree with is that in cases where a PRO is evaluated at a specific time point they recommend linear regression over ANCOVA. As mentioned above, in parallel group randomized clinical trials, ANCOVA on the PRO score adjusted for baseline score is a highly reliable way to answer the critical question whether two patients who started with the same PRO score will end with the same PRO score.