Molly Hollow Metal Cavity Ceiling Spring Toggle Hook M4 x 60 mm you link is itself "rated" to hold 25 lbs... based on it being metal and an M4 diameter. It's the drywall that isn't going to hold up to a single molly like that even if it has the finger thing that opens up when behind the wall spreading the load over more area.
if u can't make the joists suspend the load, then what u do is take a piece of wood to your liking...
- a 2x3 stud costing $1.98 per 8' if you are really cheap, cut to desired length
- a nice piece of 1x4 or 1x6 hardwood cut to desired length
- make a metal plate of sufficient area, tap screws into it which will then hold accept threaded hooks to hold the suspended load; a 1/8" thick plate could be least obtrusive.
all depends on what your goal is, permanent or temporary, nice looking or don't care
what u simply want to try to avoid is suspending the load between joists where it's going to pull on the drywall whenever possible. And when you will be using the strength of the drywall do so over a wide an area as possible and from directly underneath the joists whenever possible.
your 7 foot long projector, get a 7' length of 1x4 hardwood, use wall anchors but use many staggered every 4" or so because you would not be drilling up into joists... the drywall is going to support the load of the 1x6 by 7' long. And the hardwood then supports the weight of projector via however you hang it.
Take it down, spackle the molly holes. you could also use
mirror adhesive or any kind of drywall adhesive and glue the entire 1x4 by 7' but that would make that wood a permanent fixture on the ceiling... might look ok if painted white left there indefinitely (hang some plants or something).