Hey there SPS28,
Thank you for posting in Apple Support Communities.
It sounds like your iPhone 12 Pro Max won't charge when you plug it in. We'll be glad to assist you with your concerns.
Are you using Apple brand charging cables? If not, make sure to follow this to verify they are authentic: Identify counterfeit or uncertified Lightning connector accessories
Do you see anything in the charging port that may be blocking the connection?
Looks like you may have seen this article, but we want to make sure nothing is missed: If your iPhone or iPod touch won't charge
Be sure to follow each step in section "If your device charges slowly or won’t charge".
Take care.