I was reading some previous threads and I have a similar situation. Toilet upstairs gurgles. In addition to that and more concerning, the basement shower will not drain. Some black stuff has come up from the drain in that basement shower drain. Previous threads on this site mentioned venting. Going to try to check roof vents tomorrow, but was wondering if a vent blockage could cause gurgling and a shower drain blockage? Should I snake that basement shower drain?

Snake it from the roof and add 20' more when it reach the floor, good luck.

John

Gurgles indicate a blocked vent where the discharge attempts to vent itself by pulling air through a fdixtures trap. Hence the gurgle. Snake from the lavatory roof vent as John suggests.
Bubbles are different. They indicate a blockage where the discharge hits a blockage and bounces back sending a bubble of sewer gas ahead of it.
If the extra 20 foot of snake that john had you run out doesn't catch the blockage in the basement then snake from the shower drain. Let us know how you make out. Tom