Single entry eVisa 90 day O is an A4 PDF and the entry stamp is just a standard entry stamp with the date that they gave me to stay, in this case 90 day, based on the visa.
Due to COVID, our annual extensions had expired, so we just got a 90 O eVisa outside the country (took less than 48 hours) and then last week went along to Phuket Immigration and got a 1 year extension based on retirement. Took 20 minutes. Went back next day to collect our passports and get the the multi-entry stamp. All very painless