My iPad Mini 6 hasn’t been charged in about 2-3 months and it won’t charge anymore? Any tips?

iPad batteries must be periodically recharged if they are set-aside for storage - or if they are infrequently used - as otherwise the battery will eventually become fully depleted through self-discharge. Li-ion batteries must never be allowed to remain fully discharged, as they may irretrievably damaged and may not recover.

Batteries - Maximizing Performance - Apple

If the battery cannot be charged, the battery (or the iPad) will require replacement:

iPad Repair & Service - Apple Support

Before entertaining repair, you can attempt to restart your iPad. If your iPad is unresponsive, connect your iPad to its Power Adapter and allow the iPad to charge undisturbed for at least an hour - or preferably overnight. Then, while still connected to external power, try a forced-restart:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

If iPad still doesn’t turn on, or if it gets stuck during start up, see the Apple Support article If your iPhone, iPad, or iPod touch won’t turn on or is frozen. Or if your iPad isn’t working correctly after you restart it, see the iPad Support website.

If you continue to experience difficulties, you will need to seek assistance directly from from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/gb/app/apple-support/id1130498044

You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad:

Genius Bar Reservation and Apple Support Options - Apple

Probably just needs a battery replacement

Lithium ion batteries don't like being fully discharged.

Once you fully discharge it and leave it in that state, the battery is damaged and won't hold a charge.