I am leving in syria which we have a very bad internet and bad conction i am using tplink archer vr600 which is very bad router so I'm looking for high range wireless with AC option and MU-MIMO please advise me which router I have to buy and not that much expensive
Look at https://openwrt.org/docs/techref/hardware/soc/soc.lantiq and check for vr9/ VRX200 devices. Quite a few can be found pretty cheaply on the used market (many of them were distributed as ISP branded all-in-one devices, that may mean that the initial OpenWrt installation isn't necessarily easy). While the VRX2xx chipset is VDSL2 capable, it can be used for ADSL as well, but for that you need to find a device supporting the matching ADSL annex (A, B, J, M, ...) as that involves hardware differences (bandfilters, bootstrapping resistors, etc.).
Yes, as you can see from that list, previous lantiq generations are also supported to some extent, but I'd recommend strongly against buying those at this time (performance, ongoing OpenWrt maintenance, ...). If you don't need the feature, avoid routers with FXS ports (analogue phone ports), as those need to dedicate one CPU core for the voice functionality (hardcoded in the DTS) - and make sure to get a device with good (Atheros) wifi, as the commonly found Lantiq XWAY WAVE300 wireless chip isn't supported and the also commonly found rt2x00 based chipsets aren't that well suited for this task. If your destination uses annex A, the BT Home Hub 5 Type A might be a good and cheap option (unless shipping from the UK becomes prohibitive; read the device page beforehand, doing the initial OpenWrt installation is pretty involved (there are sellers who offer to preflash OpenWrt)).
Is there still such a thing as just the DSL modems without the built-in WiFi/router? You may be better off just getting one of these, leaving it in bridge mode and then having a complete freedom of choice for the OpenWrt-compatible router and, the possible future upgrade to a more powerful router.
At least ADSL2+ is limited to 24 MBit/s by definition (VDSL covers the range above that), that's something a lantiq VRX2xx device can easily take care of (including some advanced features), so in this particular case a dedicated modem might not be necessary (that starts to change above ~55 MBit/s WAN speeds, depending on the details).
I have used a BT Home Hub 5 Type A running OpenWrt on a VDSL2/ vectoring line with 100/40 MBit/s myself. With software flow-offloading enabled, that works reasonably well at full performance, without flow-offloading the BTHub5 tops out around 85 MBit/s. In practice I do use a more performant router, but my requirements are a bit more involved - however the BTHub5 can do this job, well.
What speed does the provider claim to offer, and what are you actually getting? You don't need GHz+ 2 core ARM, AC or MU-MIMO on a 6/0.75 Mb line. Though if you're in an apartment block or other situation with lots of neighbors, run something with 5 GHz-- stay off of 2.4 entirely.
I need the AC and Mu mimo for local streem and network
I recently bought second hand TP-LINK W8980 (lantiq chipset) which supports OpenWrt and ADSL nicely. But it's 5Ghz support is not complete and doesn't have MU-MIMO. Not sure if there is single device on the market that will fulfill your needs.
Imho it's always better to have a dedicated modem in bridge mode + a decent router running openwrt. For ADSL/ADSL2+ I would always recommend something with a BDCM xDSL chipset. It depends a little bit on the Linecard in combination with the xDSL driver version but modems with Broadcom chipsets tends to be more stable with problematic lines and usualy they also sync higher/better than devices with Lantiq/Infineon chipsets.