FL STUDIO 20.5.1 is a maintenence update to fix the issues reported with FL Studio 20.5that introduced FLEX a free synthesizer for ALL FL Studio Editions.
FL Studio 20.5.1.1188 changelog:

FLEX – Clicking the Pack name focuses the selected preset. The ‘Online packs’ section split into ‘For Download’ (for free and purchased packs) and ‘Store’ (for unpurchased packs). Improved errors when downloads fail. Various bugfixes (solving Access Violations / Crashes).
Plugin Manager – Now shows a prompt when the user wants to close the window during a plugin scan.
User data – When changing the user data location, FL Studio will offer to copy data from the old to the new location
Sytrus presets – 64 free presets by Synthwave FLEX library developer Saif Sameer.
Wrapper – Added option to allow dropping files on VST and VST3 plugins.
ZGE Visualizer – New button to reload images.
New demo project – Musata ‘Real Bass (Original Mix)’ (see video above).
General settings – ‘Associate project files’ was removed from FL Studio for macOS as it only applies to the Windows version.
Menu shortcuts – FL Studio for macOS now shows (Opt) instead of (Alt) for keyboard shortcuts.
Note: FL Studio 20.5.1.1193 changelog is not yet available.