John Collins at Ask a CFI had the most comprehensive response to what is required to be a safety pilot. The questioner is asking about being safety pilot in a Cessna 182 without a high-performance endorsement.
To be the safety pilot, you must hold a current medical or special Med. If you hold at least a third class medical, all the regulations require is that you be rated in the category and class.
91.109 (c) No person may operate a civil aircraft in simulated instrument flight unless –
(1) The other control seat is occupied by a safety pilot who possesses at least:
(i) A private pilot certificate with category and class ratings appropriate to the aircraft being flown
A C182 is an airplane category and requires a single engine-land pilot rating. There is no other requirement as long as you are not acting as PIC.
There is no requirement that you be current for IFR or VFR to carry passengers. There is no requirement that you have any endorsements for complex, high performance, tail wheel, etc.
To operate under an IFR flight plan, one of the pilots must meet the recency requirements and be able to act as PIC. You can’t act as PIC because you don’t hold a high performance endorsement. So as long as you don’t act as PIC, you may be the safety pilot.
Basic med has a quirk in the rule. This provision only applies to pilots who are acting as PIC, so when a pilot who holds Basic Med is the safety pilot, they must also act as PIC. That can be accomplished by agreement between the pilots as to who will act as PIC. In your case, if you operate using Basic Med, you could not act as PIC because you don’t have the high performance endorsement, so you would not be able to be the safety pilot.
Bottom line, if you hold at least a third class medical, you can be safety pilot without the high performance endorsement. You may not act as PIC because you lack the endorsement.