I have a couple of AP in the house that are using CapsMAN so they are connected with cable. I would like to cover the front of the house where the signal is not great but i would like to do it with some extender because i cannot get the cable there.

What are my options for using Mikrotik products? Is it possible to add another AP and connect it to my WiFi with mesh protocol?

It depends on what your devices are but the solution will still not be optimal.
What are your current APs ?
Which AP do you intend to use for receiving wifi signal ?
Only ethernet from there or again wifi ?

A ready-made option is Audience (it has 3 radios and is designed for mesh using 3th radio). But not cheap. You need 2.

If it is really not possible to put in an extra cable (really not ??), can powerline be an option ? Ethernet over power cables.
Always better then 'over the air'.
Unless you have some things like solar convertors on your network, then performance over powerline can also go down the drain (I've seen it happen myself here at home, that's when I decided to put in an extra cable from my office to the living room where the ISP router is: down the wall, into the garage, over that ceiling, into the basement, back up through the wall. Most valuable cable in my home considering cost/benefit !).

MOCA is also an option ? (Ethernet over COAX)

I have all those connected with UTP to capsman :
rb1100ahx2 - capsman
2x RB951G-2HnD - cap
wAP - cap
hAP ax²

I was thinking of getting wAP ac and connect it using Mesh. Is that something that sounds doable in my case? I need only WiFi from the new unit.

Since you have a mix of AX devices and legacy wifi devices, one single capsman for all is already out of the question. I suppose you keep AX2 separate ?
Which makes me wonder why you are using capsman ? Just an observation, nothing else.

wAP AC has two radios so you can connect using one radio to the main network and use the second one to distribute further in the house.
Legacy wifi can still be configured in repeater mode, using AX devices that's not possible (for now ?).

Your choice if you use 2.4GHz as backhaul (which I would choose since it allows for further range) or 5GHz (shorter range).
Whatever you choose, be aware the speed on the extended wifi will not be the same as for the main network (limited by 2.4GHz radio, used as backhaul or radio to connect to).

Powerline or moca are definitely no options ? It would make it quite a bit easier.

Are any MicroTik wireless available with mesh?

I think they all can to some extent. I've got a hAP AC lite sat on standby for when the internet goes down. It connects via wireless to my mobile phone hotspot. I've got it in router mode (so my LAN is separate to mobile network) but can also work as a repeater.

I assume bandwidth is reduced if you're both receiving and sending on the same antenna. However, I've got mine configured to use the 2.4GHz channel for the repeater and 5GHz for the Wi-Fi network.

Link to my instructions for setting up a Wi-Fi repeater with switch, i.e. router mode disabled:

https://docs.google.com/document/d/1D7y ... ue&sd=true