From January 2021, you can only use a PR card if you haven't been granted settled status.

You can still use your PR card to prove you acquired PR status and to show lawful residence when applying with settled status.
​ Please refer to this post for an overview of the most common issues: Issues, mistakes, errors and ommisions
Make sure you have PR, ILR or settled status.
PR, ILR or settled status.

Filling in the AN form with PR or or ILR (including Settled Status) - UKCEN Citizenship and Residence for European Nationals and their families
From January 1st, you can only use your PR card to apply if you haven't been granted settled status, otherwise, you MUST use settled status. You need to have had PR STATUS for at least a year if not married to a British spouse. See: When can I apply for citizenship?
Life in the UK test. Once passed, it does not expire. Over 65s are exempt.
Practice for your test
Book your test
The language requirement. Language tests are valid for two years. Over 65s are exempt.
The language requirement explained
See if you have a suitable degree or qualification
Are you a citizen of a majority English speaking country?
If the above doesn't apply, book your language test
Check that you meet the absences and residence criteria.
Absences and residence requirements
Gather information about your trips abroad
Allowed absences and discretion
Lawful residence (only for applicants relying on settled status)
Check that you meet the Good Character requirement
Good Character requirement
Speeding fines and awareness courses
Driving offences and parking tickets
Breaches of immigration rules
The good character guidance, treaty rights and CSI
Find two suitable referees and get their details.
Who can be a referee
Professional referees
Referee details required
Start your AN application and fill in the form online.
Online AN form and guidance
Application overview
Previous immigration applications
Biometric Residence Permits (BRPs)
Expired passports and IDs
Timescale to complete the form
Dependants and family applications
Employment and self-employment
Issues regarding names
Section 3 of the form, headed Documents, has a detailed breakdown of what the points on the checklist mean. You may want to save or print this description before moving forward, as it can be a useful reference.
Submit the form, pay and book your UKVCAS appointment.
Download a PDF of the completed form
Download the referee declarations:
Submit the form and book your UKVCAS appointment
Info about the UKVCAS services
Gather your supporting documents
Get your photos taken
Affix your photo to the referee declarations and get them to sign and date them - the forms don't need to be signed after the application is submitted, they can be signed up to a month before, as noted here: Referee details and declarations.
Gather your evidence of residence
If self-employed, provide your latest self assessment
LITUK and language test certificates and any degree certificates
Your passport and/or ID card, your spouse's ID document and marriage certificate if applicable
PR card or document with ILR stamp or endorsement, if applicable
For any other required document, look at the checklist generated by the form and the guidance.
Documents, such as marriage certificates, in a language other than English, must be translated
Upload all supporting documents to the UKVCAS interface at least two days prior to the appointment, unless your appointment includes document scanning.
What happens next
Attend your UKVCAS appointment
Applications can take up to six months, please be patient
Change of address or circumstances after you apply
Wait for the decision letter and book your ceremony. See ceremony transfers if applicable.
You are not British until after the ceremony, if you haven't been granted settled status, for example, because you applied with a PR card, you must apply for settled status before June 30th to be allowed to live here until you have your ceremony.
You should now apply for your first British passport. It is required under British law that those who have naturalised as British citizens travel in and out of the UK with a British passport.
If you have a BRP, you must return it within 5 days, see if this applies to you: Returning BRPs after the ceremony.
If you applied for citizenship with PR and haven't got settled status, you must apply for settled status while you await a decision or a ceremony invitation, before the end of June 2021: Citizenship applicants without settled status.