Can we use these sentences like 1. Solar eclipse 'must be happened' today. 2. If that happens then it 'must be occurred' at east. Are they correct ones 'must be happened' and 'must be occurred'? Or should I use 'have happened'? Also in this sentence This event must be happened by today. Is this a wrong format? I mean can't we use passive modal like must be done, must be received, etc here? BE+HAPPENED cannot come together?
No, you can't use happen in the passive voice as "be happened" (in standard and unmarked English) Similarly "be occurred" is not possible.
This is because "be happened" means that "someone happened it", and that is not a correct use of the verb happen.
It is possible to say "A solar eclipse must happen today" or "must occur". And it is possible to "This must happen by today". If you want a past form then "This must have happened by today"