To correct the problem you will have to update the client.
Playstation, search for Minecraft in library > go into settings and check for updates.
If you are an Xbox user, you will need to find the game in My apps & games > go to Options and check Updates.
Nintendo Switch, select the game > click Software Update.
PC, you'll need to go to the Microsoft Store > Downloads and updates > click Get updates.
This is all you need to know about how to fix Minecraft could not connect to outdated client error, so we hope that you will be able to fix this issue sooner rather than later.