This link leads to an X (or Twitter) post from a user who cannot be verified as any public figure or established individual in a field qualified to diagnose a person's mental state. It expands into a thread primarily focused on the user's replies to their post to expand on the claim, but each reply cities no source or evidence and uses language that would best fit the criteria for theorization.
A partial quote from the user's post which indicates such theorization: "[...]although I do think he has other early signs of it."
Additionally, in the user's further replies, they continue making sub-claims about Trump's own thoughts as to his political career and other theories based on hypotheticals.
Based on the conclusion that the user makes a direct, explicit claim that former President Donald J. Trump "is severely depressed", yet provides no supplemental sources to back this main claim or any of its following sub-claims, this is more likely than not false information.