You think Nextcloud is a linux desktop app?

Anyway, on https://nextcloud.com/partners/ for example you could talk to...

Founded in 2016 in Zurich/Switzerland, Linuxfabrik supports companies from consulting to operation and troubleshooting Linux hosts and selected Open Source Software – with technical support up to 7x24. Providing hosting with IaaS, PaaS and SaaS models in anything from virtual data centers to virtual machines in a CIS and GDPR compliant, fully self-managed, ISO 27001 certified datacenter, Linuxfabrik offers the consulting, operational excellence and expertise required for enterprises small and large.

Or maybe these

The public administration of tomorrow thinks, lives und operates closely connected. It accepts digital responsibility for processes, data and IT systems. As a strategic partner for the digital transformation of public administration, the ITEBO Group supports all administrations that are ready to face the technical, organizational, and human challenges of the digital era – as data center, software provider and consulting partner.

Or perhaps

Experience matters when it comes to IT services, and that's exactly what Si.TEK Informatica brings to the table. With over 25 years of industry expertise, they specialize in providing top- notch Internet services and taking team collaboration to the next level with NextCloud. No matter your unique needs, their team is dedicated to finding the perfect solution for you. Partner with Si.TEK Informatica for unmatched IT support and cutting-edge solutions

The list goes on.