There are essentially two types of 100% ratings (for our discussion, it doesn't matter if they are P&T or not); Schedular rating - which uses the VA Schedule for Rating Disabilities (VASRD) to rate veterans for their service-connected items (https://www.benefits.va.gov/WARMS/bookc.asp).
Yes, technically you could also have a 100% rating based on an extraschedular rating review, but that is a one-off unique and veteran specific case. And not accounted for in this discussion.
The other common 100% rating is, Total Disability Based on Individual Unemployability (TDIU). If a veteran qualifies for this program (see my Video on IU), the VA then compensates the veteran at the 100% level.
So can I work or not? With a 100% schedular rating, there is no limit on employment or income. So, yes you can work. With TDIU compensated at the 100% level, you can not work and earn above the Health and Human Services set poverty level (I know I said HUD in the video). For 2021, the 100% poverty level income limit is $12880 for the veteran themselves. It does not include other members of the household.
Be aware that the IRS and the VA databases do connect and if your income from gainful employment is over the limit, the VA will find out about it through your IRS tax filings. EDIT: I REMOVED THE REFERENCE TO MORE THAN ONE PERSON. THE LIMIT IS FOR THE VETERANS INCOME EARNED FROM GAINFUL EMPLOYMENT - NOT RETIREMENT OR SPOUSAL INCOME, BUT INVESTMENT INCOME MAY BE CONSIDERED A FORM OF SELF-EMPLOYMENT AND COULD COUNT TOWARDS THE LIMIT.
If you were TDIU but now can work, your combined VA disability rating returns to whatever it was (per the schedule) before the TDIU was applied.