重大 means "important (adj) / serious (adj)"
重点 means "focused (adj)/ focal point (n)"
Important thing might not be focused at the moment; focused thing at the moment might not be very important in the grand scheme of things
For example, stopping gun violence is an important issue, but Americans just don't focus on it at the moment; On the other hand, American is focus on the issue of 'should the football players kneel during the national anthem.' It is not an important issue compare to other real issues, but it is the focal point at the moment nonetheless.
重大事件 (and 重点事件?)
重大进展 (and 重点进展?)
重点工程 (and 重大工程? - this version sounds correct, but still is there any difference?)
重点扶持 (and 重大扶持?)
重大事件 (serious incident) and 重大进展 (important development) are valid
重点事件 (focused incident) and 重点进展 (focused development) are not valid
重点工程 (focused project) and 重大工程 (important project) are valid.
重点扶持 (focused support) is valid; 重大扶持 (serious support) is not valid