Instead of looking at share you could look at each trend separately. They're both going up, but corporate profits are going up more:

Corporate profits versus labor income https://fred.stlouisfed.org/blog/2018/08/corporate-profits-v...

Why is labor going up? In part due to more hours worked:

Nonfarm Business Sector: Hours Worked for All Workers https://fred.stlouisfed.org/series/HOANBS

If you divide labor income by hours worked, you should get hourly compensation:

Nonfarm Business Sector: Real Hourly Compensation for All Workers https://fred.stlouisfed.org/series/COMPRNFB

Working-age population is leveling off, though: https://fred.stlouisfed.org/series/LFWA64TTUSQ647S

One would expect that retirees are mostly living off capital rather than labor. Wouldn't an increased elderly population result in a lower labor share?

Or maybe something else. This paper suggests that as workers get older, they switch jobs less and get fewer raises:

"We find that a 60-year-old worker receives half the marginal product relative to when they were 20. Together with recent demographic trends, this can account for 59% of the recent decline in labor’s share of earnings in the United States."

https://www.bankofcanada.ca/2023/04/staff-working-paper-2023...

And no matter how you slice it, this is all working with national averages, which tell us little about anyone's personal situation.