@talk2tolade I received my endorsement a couple of months ago and I have used my Professors’ LOR and research endorsement to support my application.
While submitting your LOR or any other letter as part of your GT visa endorsement you need to keep in mind the main point as mentioned by @May. Te person should know your work and achievements well enough to be able to recommend you for the TG visa endorsement.
I was doing PhD and then started my own company. My PhD supervisor wrote the LOR for me, who has worked with me for 4.5 years and has known my achievements in the field. I got a separate research endorsement from another renowned Professor to endorse my research as part of optional criteria. So, this is absolutely possible.
I have provided a breakdown of evidences for my endorsement application here in case if helps: This is how I got my Endorsement for Global Talent Visa under Exceptional Talent Route (AI/ML Researcher)