Q811 was the original FLASHcode option for P25 DIGITAL CONVENTIONAL. It was later replaced with Q806 DIGITAL CONVENTIONAL (P25), which is paired with H35 in portables or G48 in mobiles for conventional operation.
Q811 might show up in the CPS feature display, but it was never a true flashcode option. It was an order option that would generate Q806 and H35 in the flashcode of, for example, a XTS2500.
"Lower" tier radios like the XTS2500/XTS1500/PR1500/MT1500, had the concept of "system packages", that you had to chose from in the catalog, with several flashcode options bundled in (and then in some cases add on other/misc options as you liked).
With "high" tier radios like the XTS5000, you could pick and choose basically a-la-carte (but of course you had to meet all the pre-reqs and deps).
Here are some screenshots from the old price pages, showing an example of the differences:
XTS5000:
XTS2500: