Why there are two users showing in uptime command results?

Try the w command. On my system I have the following:

# w
 02:16:53 up  6:48,  2 users,  load average: 0.50, 0.42, 0.52
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
pcm      tty7     :0               19:28    6:48m 16:07   0.17s gnome-session
pcm      pts/0    :0.0             01:51    0.00s  0.36s  0.76s gnome-terminal
# uptime
 02:16:56 up  6:48,  2 users,  load average: 0.50, 0.42, 0.52

tty7 is your desktop login, pts/0 is a pseudo terminal ... probably what was used to type uptime in.

Why it lists that there are two users?

Because it shows every logged in session. A single user can have multiple active sessions at any one time.

is it normal?

100% normal ... A-OK

and who is the other user, is it the root user or what?

The other user is yourself. You have multiple sessions running. You can see in your output from your question, that the user name is the same for both sessions.

I have just figured it out! I don't know whether it'll work for you or not. But I did the following steps:

1. Pressed ctrl+alt+f1 and got terminal emulator on my linux mint 20.1 (Cinnamon)
2. Typed exit and hit enter
3. Opened Terminal; typed uptime and hit enter Now, it was showing me 1 user instead of 2. Hope it helps.

Each Terminal window or tab adds an additional user to what uptime reports. So, I'm guessing that one of those users is for your current Terminal session, and the other is for your macOS.