If you like arduino boards with ATmega328, SAMD21 or ESP8266, you need USB-UART converter with DTR pin. The DTR pin is needed for uploading of your code. DTR is connected to reset pin of microcontroller.
cnx-software share a news about very cheap and small USB-UART converter with DTR pin – CH340E.
The dimension of board is only 16x16mm, it contains microUSB connector and 6 pins (5V, 3.3V, GND, TX, RX a DTR). Everything what you need for your programming.
The communication speed is tested up to 150 000 Bd.
You can buy the board on https://www.aliexpress.com/item/1PCS-CH340E-USB-to-TTL-Serial-Converter-5V-3-3V-Universal-Not-need-switching-Model-BTE17/32821571106.html
Shared from https://www.cnx-software.com/2017/10/31/wch-ch340e-is-a-tiny-10-pin-serial-to-usb-chip/
