Learn React on your own, put React on your resume, don't claim mastery over it but a vague 'know' or 'learned'. What's to lie about? But sure, it might look better in a professional context instead of just being in the keyword soup. Add at your present place a blurb: 'worked on migrating frontend to React'. You can make this true enough by simply talking to your boss "Hey, why don't we move [our native UI/command line/custom JS] to React?" and getting a "No." If it comes up in an interview, you didn't get very far and it wasn't completed. Your lack of expertise may show up in a test of ability, but then again it may not, interviews are about both sides resolving what's true enough about the resumes and the job description/requirements into what they actually care about.
And of course if you tried making a short demo as part of the learning, you can show that to the boss/the UI team, and be able to tell more in React terms how (not) far it got, though your current boss might also say "Ok" and now you have a chance to learn it more professionally. Like, that's how a lot of us learn new things -- I wanted to learn property testing, fortunately I didn't have to ask any managers (just a legal/security workflow and pom changes signed off by another team member) to add Java's QuickTheories to my team's test code. After that I used it in a few places, did a casual lunch-and-learn demo on it for the team, used it in various other places over time. I'd put property testing on my resume if a job app needed it, and just be honest that I haven't written nearly as many property tests as unit tests. It's a mindset change to write them, too, and maybe my lack of years and years and thousands of tests would be clear to someone needing such deep expertise. Or not.
And of course if you tried making a short demo as part of the learning, you can show that to the boss/the UI team, and be able to tell more in React terms how (not) far it got, though your current boss might also say "Ok" and now you have a chance to learn it more professionally. Like, that's how a lot of us learn new things -- I wanted to learn property testing, fortunately I didn't have to ask any managers (just a legal/security workflow and pom changes signed off by another team member) to add Java's QuickTheories to my team's test code. After that I used it in a few places, did a casual lunch-and-learn demo on it for the team, used it in various other places over time. I'd put property testing on my resume if a job app needed it, and just be honest that I haven't written nearly as many property tests as unit tests. It's a mindset change to write them, too, and maybe my lack of years and years and thousands of tests would be clear to someone needing such deep expertise. Or not.