Just wait for 21.02.1 which includes a fix for this (see https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=4b212b1306a93b6ebd450a4b1066ddf906035f4d for reference). In the meantime you could disable certificate checking in adblock ...
Or make your own build with openssl as your ssl backend (I'm using this lib in all of my builds).