> Do LF and Rust solicit individual donations via phone apps (or at all, really)?

"Phone apps" is irrelevant, because again, Anki was not taking donations via their app but rather via a link to OpenCollective, a separate website.

So the remaining part of your question:

> Do LF and Rust solicit individual donations (at all, really)?

Yep, the Linux Foundation has a PayPal donate button (with a simple note to U.S. taxpayers that it's not deductible): https://www.linuxfoundation.org/about/donate