If we are just talking about Google here, it sees the subdomains as separate websites so you shouldn’t have any issue with that. But we need to see the bigger picture and think if having that bit of content in a subdomain does give the right feeling to the users. For example, for Google, a subdomain of a sports website with fashion news would be two completely different websites, but the users might find it a bit odd to find content related to fashion on a subdomain of a sports website. That’s one of the reasons for having a completely different domain instead of relying on subdomains.
Google sees a subdomain as a separate domain – no SEO benefit. However, using a subdomain has a benefit if you want to cross-sell rather than moving the user to a different domain. If all the content is about the same topic and you want SEO benefit and don’t need to separate the content completely, consider using the main site’s authority with a subfolder i.e. /biology, / science /English also there are potential time and cost savings to using subfolders. hosting, managing, updating, plugins costs, etc. Something to think about.