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Visualized changing effect sizes:

UPDATE: I manipulated the effect size and here too it rapidly gets to 100% power.

Fixed slopes, changing effect size

Random slopes, changing effect size

Power for predictor 'feedback', (95% confidence interval):
      100.0% (99.54, 100.0)

Test: z-test
      Effect size for feedback is 0.10

Based on 800 simulations, (4 warnings, 0 errors)
alpha = 0.05, nrow = 6525

Time elapsed: 0 h 37 m 36 s

nb: result might be an observed power calculation

Power for predictor 'feedback', (95% confidence interval):
      100.0% (99.54, 100.0)

Test: z-test
      Effect size for feedback is 0.10

Based on 800 simulations, (4 warnings, 0 errors)
alpha = 0.05, nrow = 6525

Time elapsed: 0 h 36 m 55 s

nb: result might be an observed power calculation

sim2 <- powerSim(MLM.1.1, fixed("feedback", "z"), seed = 2, nsim = 800, alpha = .05)

Power for predictor 'feedback', (95% confidence interval):
      100.0% (99.54, 100.0)

Test: z-test
      Effect size for feedback is 0.10

Based on 800 simulations, (4 warnings, 0 errors)
alpha = 0.05, nrow = 6525

Time elapsed: 0 h 37 m 36 s

nb: result might be an observed power calculation

sim4 <- powerSim(MLM.1.2, fixed("feedback", "z"), seed = 2, nsim = 800, alpha = .05)

Power for predictor 'feedback', (95% confidence interval):
      100.0% (99.54, 100.0)

Test: z-test
      Effect size for feedback is 0.10

Based on 800 simulations, (4 warnings, 0 errors)
alpha = 0.05, nrow = 6525

Time elapsed: 0 h 36 m 55 s

nb: result might be an observed power calculation