Nothing is broken - but your WiFi network may benefit from update in either settings or improved hardware...
Your iPad is no less secure today than it was prior to the update to iPadOS14. However, your iPad is now better able to [warn] bring to your attention security deficiencies of your WiFi network and iPad settings.
This support page will describe the more secure (recommended) settings for WiFi:
Recommended settings for Wi-Fi routers and access points – Apple Support
TKIP is old and insecure - and was deprecated many years ago; it should be disabled in deference to much better WiFi security protocols (WPA2 and WPA3).
It is possible that your WiFi Router is too old to be (or not capable of being) configured for more secure settings. As such, you can either configure the most secure settings that your Router will support - or replace your Router with something more advanced that provides better security configuration options.
Whilst WPA3 is the newest standard, you should aim to use WPA2 (AES-PSK) as a minimum.
There is a also new privacy feature included within iOS/iPadOS14 that hides your physical MAC Address - and instead uses a randomly selected Private MAC Address. This feature can be enabled/disabled on your iPhone/iPad for each configured WiFi Network. This feature also has bearing upon the appearance of the Weak Security notifications.
More information about this new feature can be found here:
Use private Wi-Fi addresses in iOS 14, iPadOS 14 and watchOS 7 – Apple Support
As an alternative to replacing your Router - which, if supplied by your ISP may be impractical - you might add a more advanced upstream WiFi Router, or a WiFi Access Point, that offers mote advanced WiFi Security standards. This may be cheaper and more flexible option. One or other router will need to be configured in bridge-mode. Having added new equipment, you can simply disable WiFi on your existing router.
I hope this information and insight proves to be helpful in resolving any issues.
