iPhone 15pro keeps losing wifi connection since updating to IOS 27

Added VPN, security, or similar apps installed? If so, remove all, restart, and test anew.

You may try some of these steps, please check after each step...

1. Turn Airplane Mode On and then Off
   1. 
2. Sometimes, a simple restart can resolve temporary software glitches. Turn off your iPhone, wait for a few seconds, and then turn it back on.
   1. Restart the device. That's it.
   2. Still not solved --> Force restart iPhone - Apple Support
3. If the issue persists, you can try resetting all settings on your iPhone. This will not erase your data but will reset all personalized settings to their default values. Go to Settings > General > Transfer & Reset > Reset > Reset All Settings and confirm the action. Note that you will need to reconfigure your settings afterward. All settings—including network settings, the keyboard dictionary, the Home screen layout, location settings, privacy settings, and Apple Pay cards—are removed or reset to their defaults. No data or media are deleted.
   1. Reset All Settings: Return iPhone settings to their defaults - Apple Support:- Return iPhone settings to their defaults
   2. You can return settings to their defaults without erasing your content.
   3. If you want to save your settings, back up your iPhone before returning them to their defaults. For example, if you’re trying to solve a problem but returning settings to their defaults doesn’t help, you might want to restore your previous settings from a backup.
4. Make sure you have the latest updates installed.
   1. Update Over-the-Air (OTA) —> Update your iPhone or iPad - Apple Support (IN)
   2. Update using iTunes/Finder —> Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If none of the above steps resolve the issue, it is recommended to reach out to Apple Support or visit an authorized service center for further assistance. They can provide specific guidance based on your device model and iOS version.

Quacks wrote:

... since updating to IOS 27.

Not every issue an individual encounters on their device can be attributed to an iOS update. If the update itself were the root cause, then every device running that same version of iOS would exhibit the identical problem. In such a scenario, the forums would be flooded with countless posts reporting the same malfunction, creating an unmistakable wave of complaints that no one could possibly overlook. The absence of such widespread reports strongly indicates that the issue is not systemic, but rather specific to the device in question.

If you connect to Wifi, doesn't necessarily mean you are connected to the internet. --> Internet not available WiFi and Cellular … - Apple Community

Wi-Fi Assist is on by default. This will automatically switch to Cellular Data if the device is not connected to the internet.

About Wi-Fi Assist - Apple Support

No VPN or like apps installed.

One thing I remembered is that I dropped my phone close to when I updated.

I just removed and reinserted my SIM card. One other time I had issues (old post), but was with cellular data not working, this solved the problem. My internet is still slow on my phone :(

A dropped iPhone may well have internal damage leading to intermittent or unstable connections.

Right now... the internet is slow on my phone but on my MacBook Air M2 which I am on now, is very fast, so just did a hard reboot per SravanKrA. working better now but lost signal once and now ok again.

hard reboot Restart the device. That's it.

1. Done
2. Done
3. Not yet, only network settings as mentioned.
4. iPhone is all up to date with the latest updates.

Just turned off iphone and back on after reseating my SIM card... was slow so rebooted and now the internet is fast again. Waited a bit and now it's slow again. MacBook Air remains normal.

I guess I may have to reset all setting now to see it that solves it.

Does this iPhone connect stably to a different Wi-Fi network?

No. Was on my relative's network and noticed the same thing.