When Low Power Mode is activated on iPhones, 5G connectivity is managed differently depending on the iPhone model. For iPhone 12 and iPhone 13 models, 5G is disabled with the exception of video streaming and large downloads[2][4][7]. In these cases, using 5G is more efficient than 4G or LTE[5]. Low Power Mode also disables 5G standalone on iPhone 12 models[2][4][5].
However, the iPhone 14 series and newer models do not turn off 5G when Low Power Mode is enabled due to the improved efficiency of Apple's 5G modems and the newer devices' power management systems[5].
Low Power Mode reduces the amount of power your iPhone uses when the battery gets low[4][6]. When enabled, the battery icon in the status bar turns yellow, and the phone optimizes performance for essential tasks[4][6]. Some features may update or complete more slowly, and certain tasks might not function until Low Power Mode is deactivated or the iPhone is charged to 80% or higher, at which point Low Power Mode automatically turns off[4][6]. Low Power Mode can be toggled on or off in Settings > Battery or via the Control Center[4][6].
Citations:
[1] https://www.reddit.com/r/iPhone12Pro/comments/nmo10y/iphone_12_pro_wont_use_5g_when_low_power_mode_is/
[2] https://support.apple.com/en-us/101604
[3] https://www.phonearena.com/news/how-to-turn-off-5g-iphone-12_id128218
[4] https://support.apple.com/en-in/101604
[5] https://ios.gadgethacks.com/how-to/is-what-happens-your-iphone-every-time-you-turn-low-power-mode-0184648/
[6] https://support.apple.com/en-me/guide/iphone/iphcab9aecd1/ios
[7] https://support.apple.com/en-bh/101604
[8] https://www.reddit.com/r/iphone/comments/vlpfcv/a_full_breakdown_of_what_low_power_mode_actually/
[9] https://discussions.apple.com/thread/253475688