I think economics is a major hurdle for Ukrainian EU membership. Their GDP/capita is less than $4,000. EU average is 8x that.

I'm sure there are many other issues as well.

Negotiations, but mostly one sided. Country bordering Russia such as Ukraine have been invaded in the past during USSR time and are in fear of being invaded again (for good reasons as we all know now). They want to be part of an alliance like NATO to protect themselves, thus start the negotiation process. But NATO is aware that would be seen by Russia as a red-line to not cross, Putin has been more than clear on this topic for a while, threatening to use nukes multiple time during the last 15years or so. Because of this NATO communicated quite clearly that Ukraine won’t be able to join any time soon, which means never, but keeps negotiations open.