I’m sure yall are already on top of this, but this Reddit thread explains pretty well the fire Notion has started for people to seek alternatives.
Other than some targeted marketing strategies explaining to such angered Notion people about the Fibery vs Notion similarities/differences (aka spreading that that recent comparison article around), I would imagine prioritizing certain features that would make the transition for folks even smoother (aka ability to natively sync/import Notion page content, getting an alpha/beta bare-bones Fibery mobile app out, etc) could REALLY help Fibery capitalize on this and get more Notion-to-Fibery converts…just a thought, what do I know 
PS - although I’m a legacy free user myself for Fibery, I’m obsessed with Fibery and only don’t pay because my company teams are too old school to get out of MS word/excel/email for everything…but I know selfishly that more Fibery users + more Fibery MRR = more stability and more cool stuff in Fibery. I’ll continue to low-key “earn” and show appreciation for Fibery generously allowing my continued use of my free plan by spreading the word as much as possible myself!