Thank you very much once again for your idea @anav. I have applied your configuration suggestions to my router, and the following is what everything looks like:
After applying your scripts, I decided to test if it works this time, but it looks like it didn't. Please looks through what I have done now if I did not do something right. Thank you.
[admin@MikroTik] > ip address export
jul/29/2022 19:20:39 by RouterOS 6.47.10
software id = NKS0-DZRH
model = RB2011UiAS-2HnD
serial number = C44F0FF9C02D
/ip address
add address=192.168.10.10/24 comment=LAB-Net-WAN interface=ether1 network=192.168.10.0
add address=192.168.20.10/24 comment=Clinic-Net-WAN interface=ether7 network=192.168.20.0
add address=192.168.1.1/24 comment=LAB-Net interface=Lab-br0 network=192.168.1.0
add address=192.168.100.1/24 comment=Clinic-Net interface=Clinic-br0 network=192.168.100.0
[admin@MikroTik] > ip route export
jul/29/2022 19:20:53 by RouterOS 6.47.10
software id = NKS0-DZRH
model = RB2011UiAS-2HnD
serial number = C44F0FF9C02D
/ip route
add comment=Lab distance=1 gateway=192.168.10.1 routing-mark=Lab-Net
add comment=Clinic distance=1 gateway=192.168.20.1 routing-mark=Clinic-Net
add comment=Lab-Main distance=1 gateway=192.168.10.1
add comment=Clinic-Main distance=1 gateway=192.168.20.1
/ip route rule
add action=lookup-only-in-table src-address=192.168.1.0/24 table=Lab-Net
add action=lookup-only-in-table src-address=192.168.100.0/24 table=Clinic-Net
add dst-address=192.168.1.10/32 table=main
add dst-address=192.168.100.6/32 table=main
[admin@MikroTik] > ip firewall export
jul/29/2022 19:21:06 by RouterOS 6.47.10
software id = NKS0-DZRH
model = RB2011UiAS-2HnD
serial number = C44F0FF9C02D
/ip firewall filter
add action=accept chain=forward connection-state=established,related disabled=yes
add action=accept chain=input connection-state=established,related disabled=yes
add action=accept chain=input disabled=yes packet-size=0-128 protocol=icmp
add action=fasttrack-connection chain=forward comment="defconf: fasttrack" connection-state=established,related
add action=accept chain=forward comment="defconf: accept established,related, untracked" connection-state=established,related,untracked
add action=drop chain=forward comment="defconf: drop invalid" connection-state=invalid
add action=accept chain=forward comment="allow port forwarding" connection-nat-state=dstnat
add action=accept chain=forward dst-address=192.168.100.6 src-address=192.168.1.0/24
add action=accept chain=forward dst-address=192.168.1.10 src-address=192.168.100.0/24
add action=drop chain=forward
/ip firewall mangle
add action=mark-routing chain=prerouting disabled=yes new-routing-mark=Lab-Net src-address=192.168.1.0/24
add action=mark-routing chain=prerouting disabled=yes new-routing-mark=Clinic-Net src-address=192.168.100.0/24
/ip firewall nat
add action=masquerade chain=srcnat out-interface=ether1 src-address=192.168.1.0/24
add action=masquerade chain=srcnat out-interface=ether7 src-address=192.168.100.0/24
[admin@MikroTik] > ip dns export
jul/29/2022 19:21:21 by RouterOS 6.47.10
software id = NKS0-DZRH
model = RB2011UiAS-2HnD
serial number = C44F0FF9C02D
/ip dns
set allow-remote-requests=yes servers=80.87.78.11,80.87.78.4