In SharePoint Online, part of Office 365 offering, the way you import web parts is done differently than the traditional methods with on-premise SharePoint installations.
The way SharePoint web parts are imported with on-premise versions is you simply navigate to the web page and in edit mode, click Insert Web Part and you get presented with nice layout of web part options together with Upload a Web Part link – quick and easy.
However, in SharePoint Online environment, when you click Insert Web Part you get the following options with Silverlight control. Unfortunately, there is NO upload a web part link to be found 
.
So the way you get around this is to navigate to Site Collection Settings (or ask your Site Collection Administrator) and Web Part Galleries area.
Upload your web part file and assign the best possible group including a custom group if you wish. Once uploaded, then it becomes available to add your web part in your web page.
Hope this post saves you time if you’re faced with this situation!
Published by Chirag Patel @techChirag
Chirag is a highly experienced Chartered IT Professional consultant and Microsoft Certified Trainer (MCT) at Patel Consulting delivering business collaboration & productivity, data & information management solution implementation, migration and divestment projects with Microsoft Teams, SharePoint, Microsoft Viva, Power Platform, Security & Compliance and Microsoft 365 related technologies.
Having worked with SharePoint since 2001 and Office 365 since 2012, Chirag has covered many roles, such as Delivery Lead, Technology Specialist, Solution Architect and Trainer working with clients in Energy, Financials, IT & Communications, Professional Services, Retail, Education, Public & Third sector, which has lead him to be an exceptional consultant & trainer as quoted by clients "established himself as a leader on the project, not only delivering on the separation and migration of M365 services, but also guiding and challenging colleagues to ensure the broader set of Cloud transition activities".
Chirag is highly qualified with an MSc in Business Systems Analysis & Design and holds many certifications including Microsoft 365 Enterprise Administrator Expert and TOGAF Certified Architect.
As a volunteer, Chirag enjoys running Microsoft 365 UK (M365UK) user group and is a frequent speaker at local & international events. For his technical community contributions, Chirag has been awarded as a Microsoft Most Valuable Professional (MVP) every year since 2020. He is also an Approved Chartered Membership Assessor for BCS (British Computer Society). According to sessionize.com, he was among the top 3% of most active speakers in 2022!
View all posts by Chirag Patel @techChirag
Chirag Patel MVP MCT 
THANK YOU. Saved my life 🙂
Hi, I ran into the same issue, just found an easier solution:
Temporary disable the Silverlight add-on in your browser.
Internet options – programs – manage add-ons
You will then get the “old” method to add web parts, which allows you to upload