Support the current version of the SPFx framework (1.21.0)

[nbelyh]

Category

[x] Enhancement

[x] Bug

[ ] Question

Version

Please specify what version of the library you are using: [3.20 (latest)]

Expected / Desired Behavior / Question

The SPFx was upgraded last week to version 1.21.0
https://learn.microsoft.com/en-us/sharepoint/dev/spfx/release-1.21

I would like the SharePoint Framework React Controls to support the current (latest) release of SPFx (1.21.0)
Also, NODE 18 support stops on 30th of April 2025 (that was one of the reasons for the 1.21.0 release)

Observed Behavior

Unfortunately, it looks like most of the controls are broken with the new release (some issue with theme or style loading probably, not sure).
For example, this is how FilePicker looks with the latest version:

Steps to Reproduce

Download the current dev branch, upgrade to 1.21.0, run, and look at the controls.

[nbelyh]

Duplicate of SharePoint/sp-dev-docs#10207