Earth life may already be post-filter.

Also, I would bet on there being lots of little filters rather than one great one. Stack a dozen or so independent filters that only 1% of upstart life can develop through, and you can easily explain the apparent absence of life capable of broadcasting their existence, making life as developed as humanity extremely rare.

Maybe only 1% of stellar systems are arranged appropriately with a Jovian planet to sweep the inner system clean of killer comets and meteors. Maybe the conditions for unicellular life only occur on 1% of nominally terrestrial worlds. Maybe only 1% of unicellular life develops in a way that has a hereditary mechanism that is susceptible to random mutation, so evolution has something to work with. Maybe the jump from unicellular to multicellular is extremely unlikely to occur; it did take billions of years on Earth after all, its clearly not something that you can count on happening a week later. And maybe the chance that multicellular life develops in a direction that will eventually develop animals capable of making advanced tools is extremely rare too. Real life evolution isn't like a game of Spore, it's not a computer game with a defined goal that some force is working towards. Evolution likes robust reproducers like bugs a lot more than it likes clever monkeys. Maybe when intelligent animals do happen to evolve, they, like dolphins or octopus or corvids, almost always lack the physical characteristics necessary to put their brains towards the problem of the scientific method and industrialization. Maybe when such species even do exist, they usually socially stagnate in preindustrial times, as humanity did for a long time, and get stuck there because their culture values social stability more than innovation. Maybe only 1% manage to not nuke themselves out of existence within a few years of inventing nukes.

Stack a few of these sort of considerations up, and before long Fermi's "paradox" stops seeming very paradoxical.

The easiest filter is just that life may be incredibly difficult to get started. There's a huge complexity gap between abiotic glop and any known working cell capable of Darwinian evolution. Origin of Life research is basically various flavors of handwaving to get over this gap.

You can generate arbitrarily low probabilities for anything by stacking arbitrary fractions. If evolution has no goal, then the absence of radio loud civilizations does not demand explanation, it is only paradoxical if you implicitly believe that intelligence plus technology is a natural attractor state.