I use a Go Cruise throttle lock, but only on remote backroads where there is not a lot of traffic.
And I use it sparingly, maybe a few minutes at a time. I'll stretch and shake my hand, do a few arm circles to keep my shoulder loose.
There are other branded items that are very similar. Whichever you choose, I'd recommend a metal one with a thumbscrew adjuster to increase/decrease the grip of the device on your throttle grip.
Several good choices listed here on Amazon...
https://www.amazon.com/s?k=go+cruise+throttle+lock&crid=1T2P5A7Z5NBA5&sprefix=go+cruise%2Caps%2C165&ref=nb_sb_ss_ts-doa-p_1_9
I'd also recommend Grip Puppies foam over grips. they are really helpful in increasing your riding comfort.