Doubt concerning LVM

Due to heavy usage I need to extend my manjaro partition. My current setup is:
sda 8:0 0 465,8G 0 disk
├─sda1 8:1 0 499M 0 part
├─sda2 8:2 0 100M 0 part /boot/efi
├─sda3 8:3 0 16M 0 part
├─sda4 8:4 0 379,9G 0 part
├─sda5 8:5 0 477M 0 part
└─sda6 8:6 0 84,8G 0 part
sdb 8:16 0 447,1G 0 disk
├─sdb1 8:17 0 154,2G 0 part /
└─sdb2 8:18 0 293G 0 part

Where sdb1 is Manjaro and sda6 is ubuntu. Can I just delete ubuntu and create a new partition on sda6 creating a volume with manjaro? What should I care about?

Yes.

Well, we dont really know what your objective is here.
But … save any important data first, I guess?

I have all backed up. I wonder about how extend the partition later. Does qparted sees the lvm as a single partition after it is done?

No.
You’re mixing up terminology/different levels of abstraction: partitions will stay partitions, lvm works on top.
Partitions can be made to be physical volumes for lvm but will look the same to any partitioning tool.

Thanks for the insight.