Issues with K3s

K3S come with its own service load balancer named Klipper. You need to disable it in order to run MetalLB. To disable Klipper, run the server with the --disable servicelb option, as described in K3s documentation

Copyright © The MetalLB Contributors.
Copyright © 2021 The Linux Foundation ®. All rights reserved. The Linux Foundation has registered trademarks and uses trademarks. For a list of trademarks of The Linux Foundation, please see our Trademark Usage page