They used a lot of plugs on my work trucks, with 80 PSI in the tires, no problems.
Of course it is much better to take off the tire, inspect for internal damage, and patch the tire from the inside. That is the way that places like Les Swab will fix a flat for free. THey want you to become a customer for life, so they 'give away' free flat fix.
But for my trip to Alaska, I bought a tire plug kit from Napa. You want one with a strong thing to insert the plugs. They are not 'special' or rare as some commercials might have you think they are. Napa sells pretty good stuff. I did not want the plug tool to break off in my hand while stranded in the middle of the Alaskan Highway with some 'mechanic' willing to install a plug for me at $50 or something!
My work considered a plug a 'permanent fix' and would not replace a tire that had been plugged (even several times) until the tire tread was worn out.
If you buy the kit from Napa, the sales counter guys probably will be willing to show you how to use it at the counter. It does not take very long to learn how to use it.
Good luck,
Fred.