I have an old article (Jan 2019) about how I managed to get a Let's Encrypt SSL certificate on my Synology NAS. It's a hack built on a hack (liberal use of `chattr +i` for example!), but it has mostly worked fine for the last couple of years. However, when the cert recently came up for renewal it failed. Instead of fixing, a quick Google search shows there are much better options available now via acme.sh.
New year, new (sysadmin) me, or something like that. Step one was to fix a failing backup jobs on my Synology NAS. As usual, things escalated.