Nearby jail's signal jammer affecting cellphone and devices using 2.4GHz band
As a layman on the subject, is there something I can do to at least weaken the jammer's effect on my devices?

Sure, but it's not your job, and under any legislation I can think of, it's not your financial duty to remedy the problem. (and it's going to be rather expensive, too)
You should call your spectrum regulatory institution (FCC if you're in the US, for example).

it's not a given that the prison operates legally even on-premises, some have simply &quot;done before asking&quot; in the past (we've had dozens of people asking how to build/deploy/fix their jammers, without even as much as considering the legality of what they're doing), and
it's most definitely not OK that they jam the surroundings in the general case. FCC (or their international equivalents) should be really quick sorting that out, in my experience. &quot;Hey, I've got someone seemingly intentionally jamming in our neighborhood&quot;, without even specifying who that might be, would usually make Bundesnetzagentur send a radio surveillance car and then rather quickly issue a desist directive against the causer and quite likely also a fine.