Apple says their batteries should retain 80% capacity up to 1000 cycle counts. 80% is the threshold where diagnostics will throw a service battery warning. If the laptop is under warranty or Applecare, they will replace the battery if it hits 80% prior to 1000 cycle counts. If it is not covered, the % is when you want to pay $199 for a replacement.
in May I sent my MacBook 2017 to Apple for a warranty end battery swap. the battery went from 78% to 82% and stayed there for a couple months when I hit 700 cycles. gave it to apple at 750 cycles 80% health and they put in new battery, replaced keyboard and some ribbon cable. Now im at 30 cycles since I alternate between mb and 16 inch. I could have pushed that MB to 1000 cycles with maybe 75% life. I bet ill get another 4 years out of that battery. I'll report back in 3 years. I guess the magic to long battery life is to use it on battery almost daily but not quite discharge it all the way. maybe 5-10% of the time I let it drain to dead.