You can modify the ylabel and yticks size with matplotlib.pyplot for a specific plot, without the global options of matplotlib.

import matplotlib.pyplot as plt
plt.xlabel('This is my x text label', size = 30)
plt.ylabel('This is my y text label', size = 20)
plt.xticks(size = 20)
plt.yticks(size = 20)

I used this example from the Matplotlin documentation: https://matplotlib.org/3.3.1/gallery/shapes_and_collections/scatter.html

import numpy as np
import matplotlib.pyplot as plt

np.random.seed(1986)

N = 50
x = np.random.rand(N)
y = np.random.rand(N)
colors = np.random.rand(N)
area = (30 * np.random.rand(N))**2

plt.scatter(x, y, s=area, c=colors, alpha=0.5);

plt.xlabel('This is my X text label', size = 30);
plt.ylabel('This is my Y text label', size = 20);
plt.xticks(size = 20);
plt.yticks(size = 20);

# plt.show()      # This is not necessary for Jupyter.