Chain of trust NOT ok (expired) ISRG Root X1Let'sEncrypt

Hi Support,
Using Nextcloud 21.0.4 on Debian9/10,
after the last renewal of Let’sEncrypt certificate in the first day of september 2021, Nextcloud clients (and others clients) shown the error message “Invalid TLS certificate”.

Using “” for obtains the certs and using the option:

--preferred-chain "isrg"

is possible to solve, building the chain certs without the X1 ISRG Root certificate, leaving the SO client to produce it, with damage to older SO client…

I’ve seen that this procedure is working with some clients/servers, but not for Nextcloud clients.

Please, could you suggest me, if there are other procedures to be carried out?

Many thanks!