This has to do with the specific behavior of Android in not enforcing validity dates for root certificates, unlike those for other kinds of certificates, which are enforced. As the article you linked to explains
This solution works because Android intentionally does not enforce the expiration dates of certificates used as trust anchors.
(Certificates used as trust anchors is, in this context, another way of referring to root certificates.)
There is no way to guarantee that the other chain will work for every device or every client after September 30, but it should still work for most Android clients for the reasons described in these articles.
You are most likely using either win-acme or Certify The Web to request/renew your certificate. Both these apps will default to the correct certificate chain for Android compatibility, but you may have modified the default setting to prefer 'ISRG Root X1'.
To fix this, remove the setting specifying ISRG Root X1 as your default chain, then request your certificate again. The chain itself is stored initially in the PFX file that's built, then that PFX is stored in the windows certificate store, but from there the chain actually served by windows can vary (it can build an alternative chain that it thinks is more valid).
An alternative work-around is to switch to a different CA which has a trusted root in the (old) Android store.