Lukashenko might be able to scrap up some units of the Belarus army to attack Ukraine, but most of the military object and see the obvious danger. Any troops he sends will need to be commanded by loyalists and that leaves the ones who disagree at home in charge of troops. Belarus is soaked on three sides with western news in Russian language and it reaches into most of the country. Almost all of the colonels have access to this media and know what is really going on in Ukraine and how it will probably go sideways for the Russians pretty soon. Belarus has a small army and it cannot tip the balance, even if they went all in, the army they send could come back to haunt them with revolution. Lukashenko cheated on the last election pretty badly and there were mass protests that they had to bring Russian troops in to quell. Presumably Lukashenko, didn't want to use his own troops against his own citizens, lest the infection spread.
Putin has been putting enormous pressure on him to join the invasion, but it could lead to revolution and the Ukrainians will arm and encourage it, if they attack. The western media exposure of Belarus makes a big difference in public opinion, they see the Russian TV and the western uncensored TV by broadcast and many do, especially the elites and officers in the military. Every soldier wants as much info as he can get on what he is getting himself into.