Zabbix Appliance 4.2.6 issues with SNMP

[Orangeman]

Hello,

I'm having various issue with my newly installed appliance. I'm new in zabbix so excuse me in case the questions are stupid.
Various SNMP packages are installed, however seems not all of them, I'm missing "snmp" and also "net-snmp" I think.
I'm missing snmpwalk. Posts I've found are mostly saying to install snmp however:

# apt install snmp
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 snmp : Depends: libsnmp30 (= 5.7.3+dfsg-1ubuntu4.2) but 5.7.3+dfsg-1ubuntu4.3 is to be installed
E: Unable to correct problems, you have held broken packages.

net-snmp is not even found on included repositories.

I'm unable to solve these ones.

Also I'm trying to install some additional MIB's as I've imported Cisco ASA Template (https://share.zabbix.com/network_dev...-asa-discovery).
I'ts working but some items are showing errors like: snmp_parse_oid(): cannot parse OID "CISCO-REMOTE-ACCESS-MONITOR-MIB::crasL2LNumSessions.0".

I'm searching on the appliance and I cant find the folder where the current MIB's are to add the ones I need.

Seems that on appliance there is lot of stuff done differently, and googling these problems usually shows posts not related directly to appliance and they are mostly not applicable.

Would be anyone here so kind to help me solve these basics or give me some advice?

Thanks a lot in advance.