I want to change my home router/fw/wifi/vpn MT device. I am searching the best way to do it. I tried to make backup from the old MT and restore to the new one.
But there are some issues I have to deal with. Is there any better/preferred/best scenarion howto do it ?

Well it's very annoying that MT still don't have an easy way to move config from one device to another.
I tried to make a backup and restore on the new device and then I changed some stuff and was able to bring it to the live.
BUT I was very disapointed with one thing, when the new device seems to work fine, I made export and backup, then I tried to reset configuration, keep users and no-default-config and load that backup.rsc which WAS made on the new device and it stopped because of some uknown or missing params. WTF ?!? How is it possible, when I made export and import on the same device ?
So I have to manualy edit those rsc file many times, until MT was able to load it without errors.
Sad story

It's quite simple:

/export file=text_backup
/import file=text_backup

Import has to be monitored and text backup checked for bindings to particular nonexistend interfaces or particular MACs which obviously change when you move from one device to another.

BTW which brand allows seamless transfer of configuration between contemporay devices and ability to set the needed same version of OS to make transfer easier?

How do I copy a config that has pppoe username and password, keys, that I want to INCLUDE etc....... ??

/export verbose file=name ???

/export show-sensitive
terse optional

Do not know of certificates as have no implemented but for home router i doubt that it could be a problem ... but never say "never"

Certificates are not a problem if you don't have any. Otherwise, unfortunately, yes, because export doesn't include them.

Much thanks, dont do junk food or certificates LOL

It's quite simple:

/export file=text_backup
/import file=text_backup

Import has to be monitored and text backup checked for bindings to particular nonexistend interfaces or particular MACs which obviously change when you move from one device to another.

BTW which brand allows seamless transfer of configuration between contemporay devices and ability to set the needed same version of OS to make transfer easier?

Well, I did export on the new device, then reset config and import (on the same device] and many rows of exported backup.rsc produced error and when any error occurs during import loading is stopped. So I have to find the correct row, delete it or change it and then try to load again. It's not OK when I am unable to load config which I exported on the same device, is it ?
Regarding to trasferring of configuration, I'm not sure if there are any brand which allow it, but I'm pretty sure that Mikrotik could provide it. When I made a backup on RB951 and restore it on ax3, I was able to setup a few things by my hands to bring it to life, so why Mikrotik do not offer such a thing ? For example when importing the text backup "import file=backup.rsc --dry" to check if the rsc file is OK for loading or not ?

BACKUP/RESTORE files are not exported text files, completely different mechanism and only to be used for SAME device.

I know it's binary backup, but I tried it and somehow it works with some manual changes after restore.

As far as I know I have to change MAC addresses, order of LAN ports, wifiwave was not working (of course), but the rest seems OK.

It was a quickest way, IMHO.

Restoring a binary backup on a different device will lead to funny surprises, e.g. names of ethernet ports no longer corresponding to number on the case, or some ports not working at all. Or the PoE function no longer working.
It sure is an area where MikroTik is lacking! There should be an easier way to migrate (parts of) a configuration to another device.
That would include ignoring non-critical configuration that is not supported on the new device (like LED, LCD, SFP port), and an option to skip MAC addresses in config.

As far as I know there are three ways to do it, or I am using three ways.
1. binary backup/restore - could be tricky even on the same models, but it copy everything including certs, keys, etc...
2. txt export/import - I am using reset configuration -> no default configuration -> run after reset -> choose my txt backup.rsc, of course almost every import will stop on some kind of error, then I modify rsc and trying again until it loads OK. This way not copied certs, keys or anything like that. Even if you have a row in rsc file which manipulate with certs, it will not works until you copy/import that certs by hand before.
3. partly txt export/import - using copy/paste to Terminal. The safest way, but slowest and sometimes I missed something

So every way has its pros and cons, none of them is 100% working and none of them is perfect, but we are lazy people and we are trying to make our lives easier.

Yes, that perfectly describes the situation and possibilities.
What MikroTik really needs is a solution for the issue described in the topic: a loyal customer who had a RB951G-2HnD and now bought the exciting new hAP ax3, and wants to transfer their settings from the old to the new router without being an IT expert that dares to blank the config, connect via MAC address, and upload and import a config file, editing around problems.

(on the other hand, it may well be that the RB951G-2HnD still had an ancient firewall config and there would be benefit from starting fresh with new defaults)