While not a fix for technical crashes, a "useful feature" for managing specific event-based crashes (like the Armenia/Azerbaijan war) is found in the mod's internal settings: Miscellaneous Settings Remove existing claims to bypass specific scripting errors. Steam Community meet the mod's high requirements?
For a visual walkthrough on fixing common HOI4 mod crashes, watch this guide:
Since Hearts of Iron IV updates frequently and the Millennium Dawn (MD) mod is massive, crashes in 2021 (and subsequent years) usually stem from the same core issues: memory limits, sub-mod conflicts, or specific events bugging out.