You can do a maximum of 5 remote raids per day in Pokemon Go. This is a limit that Niantic has implemented to help keep the game balanced and fair for all players. If you try to join a raid remotely and 5 other Trainers have already joined remotely, you will be added to a new lobby. Avatars of Trainers joining remotely have a different appearance in the lobby.
There are a few ways to track your remote raid count. One way is to keep an eye on the number of Remote Raid Passes you have available. You can see this number in the Items menu. When you join a remote raid, the number of Remote Raid Passes you have remaining will be displayed on the screen.
You can also check your remote raid count by going to the Raid Battle menu and tapping on the Remote Raids tab. The number of Remote Raid Passes you have remaining will be displayed at the bottom of the screen.