Social Services used to ask me to do exactly what you are asking about and it was usually for a Dementia patient or someone who was in the early stages..
My usual approach has already been stated, remove the lock case and remove the snib. This is by far the easiest and cheapest method.
Were you to superglue it or even Epoxy the snib in place, there is a good chance that either one will come loose with the slamming of the door. The right option is to remove the snib and eliminate the chance of the the snib coming into play at some inoportune moment in the future.
The lock that Buenchico shows would not be an ideal solution for this situation as it is actually a Deadbolt and doesn't have the easy latching action that 99+ % of people have become accustomed to when closing a front door. Were you to suddenly change to that the type of lock for a Dementia patient, you will find that the door will already be open when you arrive, a front door really needs to be a latched, this gives you the most basic security.
On many occasions I have fitted two yale night latches locks on one door (snibs removed), this will usually keep someone vulnerable indoors .
If the person inside the property worries about their security and would be likely to fasten a door chain once visitors are gone. What I did was fit an ERICA .. this is a door chain even though it is engaged, it can be relased easily form outside by means of a key in a Yale type cylinder ..
https://www.locksonline.co.uk/ASEC-door-chain-with-fixing-kit.html
The one saving grace with most night latches is they are the easiest of locks to bypass. Even the chunky type Deadbolt lock would only take 30 seconds to get beyond with no keys and the simplest of tools.
Have you got a good KeySafe in place .. it is needed where you may have care staff making visits and it will save you and any others from carrying exra keys around.