A 3 month old baby can be put into a bouncer seat since baby bouncers are made for babies from newborn age to 6 months of age.
Just be sure to supervise the baby when in the bouncer.
It's not safe to just put the baby in the bouncer and go off doing something else.
If you need to do something else and cannot keep your eyes on the baby then put the baby in the crib or a playpen to keep them safe.
Babies are great but they require a lot of supervision and work to keep them safe and healthy and alive.
Never take your eyes off your baby for longer than a minute or two unless you're right there or the baby is in a crib or playpen.
Also check on your baby often as anything can happen quickly.