The 2019 and 2020 financial statements for Walmart are attached below. The 2019 statement shows 11 billion authorized shares of common stock, of which 2.9 billion were issued and outstanding as of January 31, 2019. These numbers fluctuate over the year, but only slightly. The report mentions that on March 26, 2019, Walmart had 2,869,684,230 shares of common stock issued and outstanding.
Walmart's financial statement for 2020 again shows 11 billion authorized shares of common stock, of which this time 2.8 billion were issued and outstanding as of 31 January 2019. Once again, this figure is updated to 2,832,277,220 shares of common stock issued and outstanding as of March 18, 2020.
The number of authorized shares (the maximum total number the company is able to issue) is unlikely to change from year to year, since this is specified in the articles of incorporation, which generally remain unchanged. This number can only be varied by a shareholders' vote. The issued and outstanding shares are those which have been purchased by investors. The total number is determined in the initial public offering (IPO) on the stock market. This number will increase sharply with another public offering, while minor fluctuations are often caused by the company buying back its own shares and selling them again.