will the low data mode limit to the data amount can use per month?

No, it does not limit the amount of data used. it does not set a hard cap on data use. It some background processes from using data. That may help, but it is not a true limit.

Contact your cellular carrier. They may have a way to put a hard cap on the amount of data any given line is permitted to use in the billing period.

What to expect in Low Data Mode

Different apps use different ways of reducing data usage in Low Data Mode. In general, here's what you can expect:

• Apps might stop using network data when you're not actively using them.
• Background App Refresh is turned off.
• The quality of streaming content might be reduced.
• Automatic downloads and backups are turned off.
• Services such as iCloud Photos pause updates.

Built-in iOS apps and services adapt to Low Data Mode in the following ways:

• App Store: Video autoplay, automatic updates and automatic downloads are turned off.
• Music: Automatic downloads and high-quality streaming are turned off.
• Podcasts: The frequency of feed updates is limited, and episodes are only downloaded on Wi-Fi.
• News: Article pre-fetching is turned off.
• iCloud: Updates are paused, and automatic backups and iCloud Photos updates are turned off.
• FaceTime: Video bitrate is optimised for lower bandwidth.

How to turn on Low Data Mode

1. Go to Settings and tap Mobile Data.
2. Tap Mobile Data Options, then turn on Low Data Mode.

Use Low Data Mode on your iPhone and iPad - Apple Support

Hello,

Yes Low Data mode can limit the data usage it usually makes this slower,

I recommend reading this-

Use Low Data Mode on your iPhone and iPad - Apple Support

iOS desperately needs to give us more data limit controls. It's easy to test this when you've used Android on the same phone plan and user habits, the iphone always uses more data due to background activity. I'm assuming it's imessage being enabled as well, similar to RCS on Android using data and battery in the background.

That's a good experiment: disable imessage for a month and reset your phone statistics, it will show you how much data it uses with imessage off.

For example, this is screenshot of iphone 15pro after 3 months of use (Feb - May) on low data mode, background app refresh off, icloud off. See how it's still requesting system updates in the background. I basically turn off anything that can use battery and data in the background.