There is a special version of mq2 that you can use on most private servers - the link to that is:
https://www.redguides.com/community/resources/very-vanilla-mq2-emulated-servers.60/
This is for servers that use the RoF2 client which was a specific patch of the game that was deemed to be pretty stable and was available for download through Steam so it was easy to get without resorting to piracy. There is a download link for RoF2 on this site (
https://www.redguides.com/community/threads/reign-of-fear-client.68790/) and a torrent link on the EZserver site (
http://wiki.ezserver.online/Getting_Started) if you're not worried about piracy things. Because the client doesnt get updated/patched on these private servers the same version of MQ2 will keep on working forever. I believe (hope) that mqNext is being worked on for EMU servers so we can play with all the new lovely features but I'm sure there are a lot of issues that need to be worked through to get that over the line, for now it is just MQ2.
There are private servers like p99 that dont use the RoF2 client, they use what is called the titanium client. You can't use the MQ2 available here for those servers, there is MQ2 for titanium client available in various places but I'm pretty sure it doesnt work for p99 - the client you download for p99 has specific mq2 detection built in.
I haven't played much on p99 or on any of the other private servers but I did have a lot of fun playing for a year or two on my own private server that you can set up relatively easily. I made up my own little ruleset that I stuck to and played through the expansions to OOW, there are server side bots that are sort of like pets you can set up but I eventually moved onto 54 boxing and then just made a god mode warrior character that could cast every spell and split pulls, tanked and healed myself as necessary. I'm back playing on live now after going as far as PoP because I figured I might like to do PoP flagging on a live server to then use for Artisan's Prize but I just moved on to DoDH and TSS content for the moment which isnt available on EMU.
If you are thinking of setting up your own server (you can run it on the same PC you play EQ from), this is the link
https://docs.eqemu.io/server/installation/server-installation-windows/
There are a few videos on YouTube you could follow like this one:
It generally goes pretty smoothly but sometimes people run into little hiccups for various reasons. It helps then if you know a bit of mysql to mess with the server database too. Best of luck!