I tried everything to pair my Apple pen first gen to my iPad 10th gen and the pair button is still not showing up?

Did you pay attention to this section of the article linked above?

• ”If you're pairing Apple Pencil with iPad (10th generation), make sure that you have the required USB-C to Apple Pencil Adapter and a compatible cable, such as the USB-C Charge Cable.“

See:

Pair Apple Pencil with your iPad - Apple Support

The first generation Pencil is charged and paired from iPad10 using the iPad charging cable - and an Apple USB-C to Apple Pencil Adapter:

New first generation Pencils now ship with this special adapter in the box along with the Pencil. However, some older stock purchased from retailers may lack the USB-C to Lightning adapter - and may instead have an older Lightning to Lightning Adapter.

For owners of older first generation Pencils, or for “old stock” new Pencils, the new special adapter can be purchased directly from Apple as an accessory.

https://store.apple.com/xc/product/MQLU3ZM/A