If you do not trust Tailscale as a company, here is an open source re-implementation of the server called headscale. Some/all clients are open source as well. So, you can review all components yourself or pay for a professional third-party review. Otherwise, if you take a binary blob from any origin, including Tailscale, and have it run with privileges on your server, there are few limits on what this blob can do. Yes, backdoors are technically possible, but probably bad for Tailscale’s business if that ever came to light.
Why would you study anything with literature if you had never read a book before? This sound like a colossal waste of time and money. My theory is that if you were good at anything or had an interest in a particular topic, you would study something else like engineering, medicine, or law (I exclude the case that you may be genuinely interested in literature). Thus, many of those who study literature have no idea what they should study else and probably think that they can always get through a course which is about book. Why? Probably rich family pressured them into studying instead of posting stuff on Instagram or TikTok.