How do I upload multiple Tumblr images in one post?

The Smiling Pony
Silly Pony - Celebrated the 13th anniversary of MLP:FIM, and 40 years of MLP!
Shimmering Smile - Celebrated the 10th anniversary of Equestria Girls!
Solar Hero - Went above and beyond for the Solar Deity, drawing from the power of the sun itself to bring balance to the fight against the Lunar Insurrection (April Fools 2023).
Roseluck - Had their OC in the 2023 Derpibooru Collab.
Flower Trio - Helped others get their OC into the 2023 Derpibooru Collab.
King Sombra - Celebrated the 10th anniversary of The Crystal Empire!
A Lovely Nightmare Night - Celebrated the 12th anniversary of MLP:FIM!
Princess of Love - Extra special version for those who participated in the Canterlot Wedding 10th anniversary event by contributing art.
Tree of Harmony - Drew someone's OC for the 2022 Community Collab
Elements of Harmony - Had an OC in the 2022 Community Collab

( ͠° ͟ʖ ͡° )
You need to composite the individual images into a single one. I personally use inkscape since it has a canvas that allows sorting out how to organize the images.
 
As for panels with animation, the “best practice” is to upload a still comic with a still frame of the animation, and the animated panels separately. Even if you made a composite with the animated panel included, the 256 colour limitation of the GIF format would almost certainly result in the other panels being degraded.
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