Algorithms can be beautiful to code but most of the time is not spent on this sort of thing. It's fixing null pointer exceptions or parsing json requests or whatever javascript front end engineers do.
You definitely have to prepare.
This was about him having to learn C# since it wasn't really around 20 years ago. And having to polish up Python cause it was very different 20 years ago. And other programming practices. You definitely need to stay up to date on the stuff that's relevant to your job. Not because of interviews, but because .. it's your job. If you prepare for an interview and notice that's what's holding you back, then you definitely started to grow complaceny in your job. And maybe your environment made you become that way, then it's not a good environment.
If you are up to date on this, then writing a BFS from scratch or debugging a null pointer issue or even json will be a piece of cake. Interview questions are an excuse to have a technical conversation, not to see if you remember some algo from school.
And by doing so, it profits the employees too. If everybody has been around for 20+ years but stays really current, even just for the sake of the company, their employability stays high too! It's a win-win.
These rants about "I'm back on the job market and now have to re-learn coding" tend to be a strong sign of complacency. "I already went through this and now want peace and quiet, why am I being forced to learn something new?" Well, because the world is evolving. Keep evolving with it, or gradually disappear in obsolescence. If you don't then that's not just bad for your job chances but even for your company. You'd not want to work at a place that still uses VB6 just because it was hip 20 years ago when everybody was hired.
FWIW I work at a company where we are strongly encouraged to stay on top of the game so that we stay competitive in the market. That automatically keeps everybody employable.