My game is completely up to date (the most current version as of March 31st, 2025 - I included a screenshot of the version number with the rest of my attachments), I own every pack, and I do not play with CC or Mods. I had a Sim get taken away (I had a toddler in a high chair and did not see a notification that she was hungry, but that's unimportant at the moment). I grabbed her from the manage households and returned her to my household, but I can no longer click on her.
When I looked this up in the bug reports, I saw this was reported 6 months ago but it was closed after it was tested for kids being alone after dying, but the report was about being alone after being neglected (which is the problem I am also having). I copy and pasted the exact title from that bug report.
On top of her being grayed out and making it impossible to control her, everything that should allow me to interact with her does not, outside of clicking the child and toddler care directly. I cannot click on the high chair to feed her, the toddler beds to put her to sleep, or the bathtubs to give her a bath or bubble bath. Even when I try to have her parents take care of her using the toddler care button, it is hit or miss whether or not they actually take care of the toddler.
I tried having one of her other family members adopt her as a caregiver as well as moving her out and moving her back into the household and neither thing worked. I tried going into CAS, too -- I can edit her, but not play her. I also tried saving the game and reopening it. She is still grayed out and unplayable.