Seo problem: Website with desktop and mobile version (subdomain)

Hello,

I have a problem with my website. I use a desktop version and a mobile version (subdomain with m. / eg: m.example.com) for better usability. If a mobile user gets to the desktop page, I redirect him to the mobile version. If a desktop user accesses the mobile version, I redirect him to the desktop version. I submitted my website to Google Search Console and I get a message that certain subpages are not indexed because I use automatic redirects. My question is how can I solve this problem? Switching to responsive design would not be the best solution at this point (I have a larger website). I'm pretty clueless right now.

Thanks a lot!

while I can't help you (I'm not tech-savvy, unfortunately) I would like to ask why you care about what GSC tells you! If you manage to index the "certain subpages" in any other way, that's all that matters to you. Just use an indexing service or any other method that you know works, but be willing to wait as indexing is very slow nowadays