Bottom bracket servicing
Locktite blue (also known as 243), or other similar thread lock liquids may eliminate the bottom bracket threads coming loose.

Another method to stop creaks between the BB and the frame is to use plumbers teflon tape. Just one or two wraps on the BB threads before installation will keep the bottom bracket from backing out and fill voids to eliminate movement and creaking.

Many times simply cleaning and greasing the BB and frame threads will also fix the problem.

If the problem disappears for a while after disassembling and reassembling, the bottom bracket and cranks then the BB/shell interface likely is the source of the problem...

-BUT-

Creaks can come from many sources yet they will sound like they are coming from the bottom bracket.  Some other common sources to check:

Cassette: Tighten down the lockring. I've had this happen to me a couple times.

Seat rails were sliding where they went inside the saddle.  The creaking disappeared when I stood.

Handlebars creaking inside the stem. Fix by lubing the bars and reinstalling.

Stem to steer creaking. Disassemble, clean, grease, reassemble.

Chainrings on crankset: Loosen and retighten the chainring bolts.

My recommendation is to fix one item, see if the creak persists and if so move on to the next.