Is My Iphone 6 Plus Compatible with IOS 13?

No. 12.4.3 is the last version for an iPhone 6/6Plus.

kaye ~ You can find answers to such questions by searching Apple's Knowledge Base here:

https://support.apple.com/kb/index?page=search&locale=en_US

...and finding this Support Article:

iOS 13 and iPadOS are compatible with these devices

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Alancito wrote:

kaye ~ You can find answers to such questions by searching Apple's Knowledge Base here:

Or you can just ask in this user-to-user forum, which takes less time than trying to find sometimes obscure knowledge base articles. 😏