It's not about immigration as such, it's about asylum seekers.
Brexit happened because so many Eastern Europeans came to the UK keeping wages low and competing for work. At least that was the catalyst.
After Brexit, the government continued to bring in large amounts of immigrants. But what changed were people crossing the channel from France in small boats.
Many of these people are fleeing Afghanistan and Iran but some are economic migrants from Vietnam and Albania. The UK struck a deal with Albania to return people so they don't come anymore.
Many of the people on the boats destroy their ID so it's difficult to process them. The immigration department has also been starved of funds meaning that claims are taking years.
Even though these people are only about 3% of annual immigration, they've become a lightening rod for everything wrong in the UK.
Many are male and Muslim and the government and media have created a lot of division leading to tension. Things got so bad that during the riots they tried to burn down a hotel with asylum seekers inside.
The riots weren't about immigration as such, the Southport murderer was rumoured to be a Muslim asylum seeker.