Part-time arrangements here ("national carrier" with turboprops. two narrow body jet fleets and a small long-haul operation):
Salary, number of working days, maximum flight/duty hours and overtime limits pro-rated with the same factor as the salary.
"Sweet spot" for the company is around 80% as this actually allows for higher productivity than full-time because rest time/minimum days off restrictions are less limiting. Below that fixed costs (training, uniform) start to become a burden.
While there are 1 month off - 1 month on and similar options, most part-time is done by just reducing the number of working days per month.
Overall it's quite popular with many pilots working 80-90%. The minimum is 60% (70% for long-haul) except for parental part-time.
Access to part-time is easy after the first two years. The company has a temporary recall option and there's a right to return to full-time (or more work) if the company hires.
There's also subsidized part-time from age 55, with 50% flying and 60% pay and 70% flying and 80% pay. Whether this makes sense economically for the company depends a lot on pay scales, age and career progression.
Good luck.