as a joining condition is forced to adopt the Euro
That doesn’t happen. The treaties can force a country to join the eurozone once they meet the convergence criteria. But the convergence criteria include being part of ERM II for at least 2 years. Participating in ERM II is not mandatory, so countries can simply choose not to, and thus never meet the criteria for adopting the Euro.
For example, out of the six EU countries currently not in the eurozone, only one is participating in ERM II (Bulgaria).
Edit: and there are always opt-outs too. Denmark for example opted out of the Eurozone.
That doesn’t happen. The treaties can force a country to join the eurozone once they meet the convergence criteria. But the convergence criteria include being part of ERM II for at least 2 years. Participating in ERM II is not mandatory, so countries can simply choose not to, and thus never meet the criteria for adopting the Euro.
For example, out of the six EU countries currently not in the eurozone, only one is participating in ERM II (Bulgaria).
Edit: and there are always opt-outs too. Denmark for example opted out of the Eurozone.