On Saturday, July 25th, 2020 and Sunday, July 26th, 2020, Pokémon GO Fest 2020 is set to take place! A T-shirt commemorating this event will appear at the Pokémon Center on Saturday, July 11th, 2020. Let's wear this T-shirt and get in the mood for the event! Also, "Pokémon GO" will have an in-game t-shirt item with the same design, so look forward to it. The Pokémon Center Online will start selling the t-shirt starting on Thursday, July 9th, 2020 at 10:00 a.m. The sale of this product may be postponed or cancelled depending on the situation.
Source:
https://www.pokemon.co.jp/info/2020/06/200626_gd01.html