That is on purpose, there was a change in debian introduced by some systemd-behavior change. Now they boot in VT1 and switch to graphical (VT7 in siduction), but don't free VT1 for subsequent use. There was a reason for that and I read about it, but forgot what it was....
You can use all the other terminals (STRG+ALT+F2-F6), of course, and cycling through tty2-6 +graphical 7 with ALT F2-F7.