What is the max level in Raise an Anomaly?
Unpublished. Official art shows a Level 99999 label. That is not enough to call 99999 the cap.
Progression
Read Raise an Anomaly levels from official art without treating marketing numbers as a confirmed cap.
Updated

Raise an Anomaly levels are the growth axis the official page names when it says to feed baby anomalies to level them up. Levels are not a skill tree and not a weapon upgrade path.
This page owns the level / age / day labels on official art. Feeding as a verb lives on the food page so the two keywords stay apart.
One promotional piece prints Level 1, Level 50, and Level 99999 on a yellow smiler body that gets taller and more detailed. That is official media, not an in-game settings panel.
Treat 99999 as marketing. Publishing it as the cap would be a guess. If an in-game UI later shows a real cap, this page will switch.

A second piece prints Age 1 (bath) and Age 100 (hallway adult). Age may be flavour for the same growth, or a second counter. The store page only says “level them up.”
Until a HUD shows both Age and Level at once, do not theorycraft a dual-XP system.

A third piece prints Day 01 as a small ball creature and Day 100 as a forest giant. Days read like session time or world time, not like a menu stat.
Useful takeaway: leaving an anomaly alive for a long time is part of the fantasy. Exact cash at Day 100 is unpublished.

Official answer: feed babies. Community answer: Food Shop SKUs plus time on the plot. There is no public XP curve, including for Fairy Cake and Eyeball Soup.
The X2 GROWTH SPEED pass, when sold, claims eggs grow 2x faster. That is egg growth, which may or may not be the same counter as anomaly Level. Do not merge those words without a UI.
Your first goal is not Level 99999. It is a baby that has been fed at least once and is printing cash for the next steal.
When a HUD number is captured, this page will add a table. Until then, “higher is better” is the only safe rank.
FAQ
Unpublished. Official art shows a Level 99999 label. That is not enough to call 99999 the cap.
Unknown. Both appear on official media. The store page only mentions levelling by feeding.