How long do LiPo batteries last?

Depends on the chemistry inside and how you determine “last”. LiPo is a form factor, not a chemistry, kind of like saying I have cookies in a plastic bag vs a cookie tin amd asking someone how many calories are in each cookie?

If using a typical portable electronic device, they will be between 70–80% capacity after 500-1000 cycles IF the use pattern is the same as a typical cell phone.

Generally, 18 months to 24 months is when it is useable.

Now you can make them last longer by:

Not fast charging them
Not draining down to 0%
Not charging to 100%
Keeping them as close to room temp as possible.. (I.e. don’t leave them on a pool deck mid summer or go for a long run and then decide to charge it while it is ice cold)