J-Link RTT – Real Time Transfer
wiki.segger.com: RTT

C:\Program Files\SEGGER\JLink\Samples\RTT\SEGGER_RTT_V754d.zip

platformio

Segger RTT Library: printf debugging on Arduinos with arm processors
koendv/RTT Stream

lib_deps =  
	koendv/RTT Stream

--- Available filters and text transformations: colorize, debug, default, direct, hexlify, log2file, nocontrol, printable, send_on_enter, time
--- More details at https://bit.ly/pio-monitor-filters
--- Miniterm on socket://localhost:19021  9600,8,N,1 ---
--- Quit: Ctrl+C | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---
SEGGER J-Link V7.50a - Real time terminal output
SEGGER J-Link EDU V10.1, SN=XXXXXXXXX
Process: JLinkGDBServerCL.exe
setup!
loop!
loop!
loop!