Realistically, reducing immigration even modestly is not going to happen unless Brits are OK with working several more years on average, and prepared to keep themselves in physically better shape so that they are able to do so.
I don't see much sign of this happening, though.
The Nordic and many East Asian countries seem to be able to manage OK-ish with less immigration, for the moment. (I know Sweden has quite a bit of immigration, but that seems to be about "being kind to refugees" rather than desperately trying to fill vacant posts). But these are countries where populations are slimmer, sprier and healthier into old age - more walking, better diet. And people of all ages have a more austere work ethic. Not saying that's always a good thing, to be honest, but it probably does help when it comes to getting older folk to stay in the workforce longer.
Meanwhile, in the UK, years of "healthy life expectancy" have gone down slightly, not up, in recent years, and obesity rates are worse than ever following the pandemic. I'm always seeing posts on here about people saying "AIBU to retire at 53?" The responses are generally along the lines of "as long as you've got the money, GO FOR IT, girl!" Of course, people do have the right to retire early if they have the private means to afford to do so. Just making the point that if you are a society which is broadly OK with this and is not inclined to shame those who retire from the workforce early, you'll need more immigration to fill the gaps.