"unstable" can mean many things with a DSL connection - can you be more descriptive about the symptoms?
Your upstream data rate is very low given the reported noise margin - what speeds does your ISP say you should get? Even your downstream noise margin is a bit higher than would normally be expected (6-6.5dB). For comparison, what connection information does your TD-W9970v3 give?
You might want to consider adding a hotplug script to log DSL status changes which might help with diagnosing any problems.
Are you using the xDSL modem firmware "blob" distributed with OpenWrt images or have you installed an alternative one? You might want to check this thread and consider testing alternative xDSL firmwares.
As your VDSL connection doesn't appear to require vectoring support, the updates and fixes to this functionality in OpenWrt 22.03 aren't likely to help but you might consider trying it out anyway and pick up the security and other fixes. You can use a vectoring capable xDSL firmware on a non-vectoring connection, so running 22.03 would also give you a wider selection of alternative versions to evaluate.