Yes, daemon and client needs be same major version number. A quick google search reveals instructions for this(getting deluge 1.3.15 on ubuntu's offering only deluge 2.0.3), and little further down in thread, verified instructions specifically for ubuntu 20.04:
https://askubuntu.com/questions/1184176/how-to-install-specific-older-version-of-deluge-with-all-the-dependenciesEdit: Sorry, reread your post and mistook ubuntu 20.04 for 20.10 before, though try anyway as probably same instructions, or atleast very close to, as is just wget'ing old packages from bionic repo and apt installing them, and/or google it, e.g my posted link was second result where first was a reddit poster asking same question but unanswered(and I as said mistook your ubuntu version so searched for "ubuntu 20.04 how get deluge 1.3.15").