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If anything, I would think their 'Great Filter' would be the ability to move outside of your solar system, especially finding/arriving at another one capable of supporting your life. The closest possible Earth-like planet we've found is 13 light-years away. If it's even capable of supporting life. Assuming we could manage even half-lightspeed travel, that's 26 YEARS of traveling, which would require some very dedicated people. And quite a lot of them, to successfully colonize, and reproduce and be able to expand without inter-genetic issues. All of whom need to survive that trip, not just physically but mentally as well. How do you shield against galactic cosmic rays? How do you feed and water everyone? How do people not go crazy being cooped up in their spaceship for years?

I would hazard a guess that there are plenty of civilizations that have reached our level. Many that have probably been able to terraform their Venuses and Mars-es. But making it to another star system is a massive step above that.

Very good point! Had never thought of that as being a filter. How many Type II civilizations, having exhausted the resources of their home system, can take the next big step?

To them, it may not be such an enormous leap, being perhaps millions of years more technologically advanced than we are. But to us, it seems almost insurmountable, and may actually be the greatest Great Filter of all.