How to go past window 9 in GNU Screen without going to Window list?

If you type Ctrl+a+' (an apostrophe), screen asks you to enter the window number. It's in screen help on the left side. Hit Ctrl+a+? to see the help.

According to screen's manual page, you can add the following lines to your ~/.screenrc file:

bind -c demo1 0 select 10
bind -c demo1 1 select 11
bind -c demo1 2 select 12
bindkey "^B" command -c demo1

makes C-b 0 select window 10, C-b 1 window 11, etc. Alternatively, you can use:

bind -c demo2 0 select 10
bind -c demo2 1 select 11
bind -c demo2 2 select 12
bind - command -c demo2

makes C-a - 0 select window 10, C-a - 1 window 11, etc.

Well I don't know what your doing that actually needs 10+ processes to be accessible in one screen instance anyway, but you might just use ctrl-a n/p to go back and forth (which conveniently wraps around).

And consider just using 2 instances of screen ... or even a screen-in-screen

There is no way to switch directly to windows above number 9 as explained in the doc.