Same here in the US. Forums like HN and /r/cscareerquestions overrate how many people do OSS or care about it. I think maybe 5% of devs I've worked with do anything beyond the 9-5.
I never quite understood that advice. I've worked for multiple FAANGs and have no OSS or really any online presence tied to my name. Just practicing interview-like problems in an interview-like setting is a far more efficient use of time than doing random OSS work if the end goal is to get hired. Those companies really don't even look at your commits to their own codebase when they are considering promoting you - they aren't going to delve through your open source projects to hire you.
Just do things like implement a heap or boyer-moore in pseudocode or python on pen and paper without referring to google.
cscareerquestions is heavily weighted towards graduates fighting tooth and nail to secure a first job with companies that mostly view them as an undifferentiated commodity. There's way more supply than demand.
It probably is a better way for graduates to differentiate themselves than experienced engineers.
Just do things like implement a heap or boyer-moore in pseudocode or python on pen and paper without referring to google.