In 2020, Ukraine spent $6 billion on defense and had mostly old Soviet equipment. In 2020 Germany spent $53 billion and has modern fighters and tanks. If the Russian Army that was still whole couldn't take Ukraine, what on earth makes you think the Russian army that has lost thousands of armored vehicles, a couple hundred thousand men, and almost all their trucks, can conquer Germany?
Or even more, the UK where they would have to conduct a sea invasion.

German defence minister says his country cannot protect itself in war
The Germany Defence Minister said the army of his country is understaffed and does not have adequate equipment as it has been neglected from the federal government for decades

Britain can no longer defend itself
When the Berlin Wall fell, the British Army had 152,800 soldiers. Tony Blair’s government cut this to 110,000; David Cameron’s reduced it to 87,000. Plans to let that number fall to 82,000 were accelerated by the former defence secretary Ben Wallace. It’s generally accepted that by next year...
