If that's really the reason it happened, the fix (for now) is obvious: flash the regular boot.img that comes with this particular LineageOS buildI just installed the newest build today. But when i rooted with magisk, wifi stopped working. any fix?

From the device's LOS page
Then use fastboot to flash it, that means you replace the Magisk-rooted boot.img back with regular one
Also, this will confirm that it's truly the reason, in case your wifi works immediately after this revert.. it can be worth to collect a logcat before reverting the boot image, so you capture any error/exception that helps the maintainer @EdwinMoq investigate this as a bug.