Ltd company from 2017 how far back can I claim expenses?

Msjf

Was the company incorporated in the 2018-19 tax year or 2019-20?  Have you lodged first accounts yet with Companies House?

Are you doing everything on a DIY basis? Do you have a business bank account in the Company name and have you or someone on the Company's behalf been logging expenses and keeping digital/paper receipts?

If you are the/a Director, can your Company Secretary help sort out the financial side of things including sourcing some professional advice?  You both have duties relating to the Company offices you hold and must quickly get up to speed on these so that you don't jeopardise what you are hoping to achieve with the product you are developing. It's great you're doing something creative, but you need to approach the business side of things in a structured way and should already know about the annual cycle of company reporting and tax return obligations.

Get quotes by phone then in writing from small business accountants in your area who have been recommended by business owners you know.  If you have lots of questions and don't want to research the answers via gov.uk, prepare a list and see if you can set up an initial meeting (via Zoom/Teams) with an accountant for a set fee, if they don't do a free initial consultation.

bris

Are all the invoices in the ltd co's name? Paid for from the companies bank account? It could be a directors loan which would be the easiest way, but as others have said a real accountant would look at how these payments were made and see if it can be claimed as an expense or added to the directors loan account.