Indeed, Excel can be used as the primary program /tool in a Laboratory Information Management System, if it will achieve the purpose for your laboratory. In fact, the Advisera ISO 17025 toolkit provides templates as either Microsoft Word or Excel. The toolkit can serve as the core documentation for your LIMS system.
A LIMS is typically made up of a combination of noncomputerized (hardcopy records) and computerised systems. The computerised system can range from a simple system of stored scanned Pdf format records and Microsoft Word and Excel documents, forms and records; to more complex direct data transfer, processing and storage between instruments and database programmes. As long as the requirements for the LIMS are identified, scope defined (what it does) and it is tested and validated for functionality - then that is an acceptable framework. Functional validation involves test cases to provide evidence that the system does what it is meant to do. All the requirements for data and information control must be met. That includes protection, access and change control, integrity and recording system failures. Furthermore, all calculations and data transfers must be checked and safeguarded.
For more detail on what is required for ISO 17025, read the whitepaper Clause-by-clause explanation of ISO 17025:2017 available for download from https://advisera.com/17025academy/free-downloads/ and preview the toolkit at https://advisera.com/17025academy/iso-17025-documentation-toolkit/