How do I set a static IP in Ubuntu 20.04.3 LTS?

I'm trying to set up a lab computer as a ssh server following this guide. One of the steps is setting up a static IP address. So, I was glad to find this answer. Following it, I created /etc/netplan/50-cloud-init.yaml file, pasted

network:
    ethernets:
        enp0s3:
            addresses: [desired_ip_address/24]
            gateway4: my_router_ip_address
            dhcp4: no
            nameservers:
              addresses: [1.1.1.1,8.8.8.8]
            optional: true
    version: 2

and run

sudo ip addr flush my_ethernet_num
sudo systemctl restart networking.service

where my_ethernet_num == enp9s0. Buuuut, after this ip a showed no ip address for the Ethernet:

svyatoslav@svyatoslav-desktop ~> ip a                                    (base) 
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp9s0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether a8:a1:59:4b:e8:bb brd ff:ff:ff:ff:ff:ff
3: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default 
    link/ether 02:42:f3:38:2f:33 brd ff:ff:ff:ff:ff:ff
    inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
       valid_lft forever preferred_lft forever

and sudo lshw -C network yielded *-network DISABLED. Then I tried to use that guide (section 'Static IP Address Assignment'). I created /etc/netplan/99_config.yaml, pasted the necessary code, run sudo netplan apply. Nothing changed except that I STOPPED SEEING wired connections in network settings... I tried the answer from here, and the 'Wired' section returned. But I can't change anything (for example, I can't pick 'Manual' option) screenshot.

So, the questions are: how can I return the ability of changing it (in order to follow one more guide), or is there any other solution that will succeed in setting static ip address?...

--EDIT from 12/05/2021--

Here are all of my .yaml files showed by ls -al /etc/netplan:

01-network-manager-all.yaml:

# Let NetworkManager manage all devices on this system
network:
  version: 2
  renderer: NetworkManager

50-cloud-init.yaml:

network:
  ethernets:
    enp0s3:
      adresses: [192.168.0.116/24]
      gateway: 93.175.20.231
      dhcp4: no
      nameservers:
        addresses: [1.1.1.1,8.8.8.8]
      optional: true
  version: 2

99_config.yaml:

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      addresses:
        - 192.168.0.116/24
      gateway4: 192.168.0.1
      nameservers:
        search: [mydomain, otherdomain]
        addresses: [192.168.0.1, 8.8.8.8]