What are best picture settings for Nintendo Switch, Ps4 Pro, and Xbox One X when connected to TOSHIBA 4K, 2019 TV (TOSHIBA_50LF621U19)?

With pretty much any modern TV, there's a, "Game Mode" setting. That setting's all about minimizing input latency by bypassing one or more video signal processors other video sources usually use. It generally has fewer picture settings and may not be as customizable, but if you care about your inputs happening as soon as you press the button instead of perhaps a frame or two later, it's essential. Just go with that and adjust the colors how you like.