If you're planning on staying in Europe for more than 90 days, you'll need to apply for a long-stay visa. The requirements for these visas vary depending on your nationality and the country you're applying to, so it's important to do your research well in advance.
In most cases, you'll need to provide:
A valid passport
A completed visa application form
Proof of financial means (e.g., bank statements, employment contract, etc.)
Proof of accommodation (e.g., a lease agreement)
Health insurance
Depending on the country you're applying to, you may also need to provide other documents, such as:
A criminal record check
A medical certificate
Language proficiency test results
If your visa application is successful, you'll be issued a long-stay visa that will allow you to stay in Europe for the specified period of time. Please note that long-stay visas are not renewable, so if you need to stay longer, you'll need to apply for a new visa before the current one expires.
Option 2: Leave the Schengen Area and re-enter
If you don't want to apply for a long-stay visa, you can also stay in Europe for more than 90 days by leaving the Schengen Area and then re-entering. The Schengen Area includes most European countries, but there are a few exceptions, such as the UK, Ireland, and Croatia.
To do this, you'll need to spend at least 90 days in a non-Schengen Area country, such as:
Albania
Andorra
Bosnia and Herzegovina
Bulgaria
Croatia
Cyprus
Kosovo
Moldova
Montenegro
North Macedonia
Romania
Russia
Serbia
Turkey
Ukraine
Once you've spent 90 days in a non-Schengen Area country, you can return to the Schengen Area and start a new 90-day period. Please note that this process can only be repeated once every 180 days, so if you want to stay in Europe for more than 180 days, you'll need to apply for a long-stay visa.