Firstly, the World Cup should never have been given to Russia and having been wrongly done so, should have been taken away from them long before now. For footballing and organisation reasons, they didn't deserve it - their stadium, infrastructure, logistics etc. don't compare to ours and several of the other competitors. They have issues such as hooliganism, racism, homophobia etc. in football and in society that have largely been dealt with here and in some other countries. They are corrupt to the core (which is probably why they got the world cup) and off of the pitch have assisted directly and indirectly genocide in Syria, have annexed and invaded other countries, cheated in sport through doping - proven state sponsored and organised doping, which is in addition to the recent poisoning in Salisbury (not the first example of that in the UK and elsewhere in recent times) - not only doing so on another countries sovereign territory, but meaning several dozen people have been hospitalised.
As I say, Fifa should have taken away the World Cup from them ages ago and, having not done that (as they haven't changed one bit and are every bit as corrupt still as Russia, Qatar and half of the members who vote them in time and time again) we and other top footballing nations should have acted and pledged to boycot the World Cup in Russia, break away from Fifa etc. etc.. However, the opportunity for that and momentum seems to be gone and yet again Fifa have wormed their way out of corruption again, changed nothing and have maintained a system of largely corrupt nations voting in a largely corrupt Fifa leadership and then receiving perks for so doing (such as the 2026 World Cup being extended to give even more undeserving countries a chance to qualify).
That's not saying we shouldn't withdraw from Fifa or boycott the Russian (and Qatar) World Cups, but we'd be a lone voice and it would make no difference and Fifa, Russia and, for example, chip on your shoulder African nations would just rally against us.
My understanding is that the government proposals to boycott the World Cup are from, understandable, safety angles. If the Russians can poison people in the UK and hospitalise dozens of citizens, what can the state there - whether it be the police, army or state sponsored and trained hooligans do to our players, officials and fans? I suspect the team will go, but fans will be discouraged from going and we won't send the usual diplomats or army off officials (who will probably be replaced by security and undercover agents etc.)