Offline raspberry and IP addess

Question

I am trying to use my raspberry through SSH, in order to connect to it I wanted to set a static IP address for it. While being connected to my home network, it works fine, the IP is probably set by my router So i can access it easily. But when offline it just won't connect. I have installed RaspAP and this service also doesn't work properly without a network access so wlan0 interface is not usable.

I have tried to configure my dhcpcd.conf file in order to configure a static IP address for eth0. I am very new in terms of network connections and such, and as RaspAP uses dhcpcd, I was told not to configure /etc/network/interfaces

Do you have any tips or something I should look into?

EDIT2:

When I plug in my ethernet cable from PC to raspberry I can access it with SSH for a brief 5 second then the connection is shut down.

This is what ip a shows:

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: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether b8:27:eb:e7:22:be brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.126/24 brd 192.168.1.255 scope global noprefixroute eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::9df9:aefa:d435:4c68/64 scope link
       valid_lft forever preferred_lft forever
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether b8:27:eb:b2:77:eb brd ff:ff:ff:ff:ff:ff
    inet 10.3.141.1/24 brd 10.3.141.255 scope global noprefixroute wlan0
       valid_lft forever preferred_lft forever
    inet6 fe80::bf7e:a6b4:72eb:14cd/64 scope link
       valid_lft forever preferred_lft forever

ip r

default via 192.168.1.1 dev eth0 src 192.168.1.126 metric 202
default via 10.3.141.1 dev wlan0 src 10.3.141.1 metric 303
10.3.141.0/24 dev wlan0 proto dhcp scope link src 10.3.141.1 metric 303
192.168.1.0/24 dev eth0 proto dhcp scope link src 192.168.1.126 metric 202

When I say offline, I mean my computer AND my raspberry are both not connected to the internet/home network/router. The only physical connection I want is an ethernet cable connecting both devices.

Update:

When the RPI and the PC are connected together with an ethernet cable, Wireshark throws these messages from the raspberry:

Who has 192.168.1.1? Tell 192.168.1.126

Why is the raspberry trying to find the router? there isn't one...

Answer 1

So by reading the last line of my post, it raised a question in my head:

When the RPI and the PC are connected together with an ethernet cable, Wireshark throws these messages from the raspberry:

Who has 192.168.1.1? Tell 192.168.1.126

Why is the raspberry trying to find the router? there isn't one..

I manually set the dhcp settings of my computer in adapter/IPv4 protocol, to a static gateway by default (same as the router the RPI is trying to find). My rasp would try to connect and somehow, it works fine now.