Lukashenko doesn't have broad public support in Belarus. There also doesn't seem to be support for the Russian invasion / attempted takeover of Ukraine in Belarus, although all I have to point at is the spate of rail sabotage in the early days of the invasion.

I'd expect Belarus to allow Russia to put bases on its territory, possibly fly planes that launch missiles and drones that target Ukranian civilian infrastructure from there, but anything that requires logistics to flow through Belarus is improbable - first because it's a giant swamp and Ukraine has already interrupted roads and rail through there, and second because logistics by rail would present an attractive target (also trucks on the road, but we all know how poorly the RF does with road bound logistics). I don't see Belarussians halting tank columns, but anything susceptible to an IED