How about solving it with code like below?

public class CustomPreference extends Preference {
    
    ..............

    @Override
    public void onBindViewHolder(@NonNull PreferenceViewHolder holder) {
        super.onBindViewHolder(holder);

        TextView tv (TextView)holder.findViewById(android.R.id.summary);
        if(tv != null) {
            if(mSummaryTextSize > 0) tv.setTextSize(mSummaryTextSize);
        }
    }

    private int mSummaryTextSize = 0;
    public void setSummaryTextSize(int size) {
        if(mSummaryTextSize != size) {
            mSummaryTextSize = size;
            notifyChanged();
        }
    }
}